Spitz? Phelps? The Thorpedo? Who is the best?

Michael Phelps has accomplished more in swimming than he ever imagined. He has Olympic gold -- six times over. He has world records -- even while sporting a goatee. He has achieved international fame and endorsements galore.

But there is one title he's really after: Becoming one of the greatest swimmers of all time, if not the greatest.

In the minds of some swimming experts, Phelps has already achieved that goal. . Even though Phelps didn't break Mark Spitz's record of seven Olympic gold medals in 1972, some believe Phelps' achievements are even more remarkable because swimmers are more specialized than ever.

Phelps has brought more attention to the sport in the United States and was the media star of the 2004 Games in Athens. This past week in Melbourne, he out-performed Aussie hero Ian Thorpe by claiming seven gold medals in one World Championship meet. Phelps fell one gold short of his goal, but it wasn't due to his own swimming. Ian Crocker DQ'ed in a relay, costing the Americans a medal.

So where does Phelps stand?

Is he better than Ian Thorpe, the recently retired Australian star who has five Olympic golds and 24 Olympic and world medals? Are Phelps' achievements better than those of Matt Biondi, who captured eight gold medals over three Olympiads, five of which came in 1988?

Where does a specialized swimmer like Aaron Peirsol fit in? He's an expert backstroker who has three Olympic golds and, prior to these World Championships, he had not lost in the 200 back in an international meet since 2000. (His streak ended in Melbourne with a silver in that event, but he did win gold and set a world record in the 100 back.)

And how do you compare eras? How does one compare a swimmer like Charles Daniel, who won five golds over three Olympics in 1904, 1906 and 1908, to swimmers of this generation? Where does Johnny Weissmuller, the "Olympic Tarzan" who never lost an official race in his career, fit in?

"I think it is hard to say that somebody is the best swimmer of all time," said Brendan Hansen, who owns world records in the 100 and 200 breaststroke. "The best way for me to describe Michael is that he is a clutch guy. When he gets into a pressure situation, he performs and that makes him a great swimmer.

"With the different areas and categories of swimming, I don't think you can outright call any swimmer the greatest swimmer of all time. There is probably some 12-year-old out there that will do better at some point."

What could set Phelps apart from the pack? Why, what else? The never-ending quest for more.

And if Olympic gold medals are indeed the gold standard, then Phelps could blow everyone out of the water. Phelps could win eight Olympic golds in Beijing and has said he plans on competing in the 2012 Olympics in London.

"You could argue that Michael is the best swimmer of all time," Peirsol said. "I certainly do think he is one of the most well-rounded as far as being complete. He is one of the most complete swimmers I have ever seen."

Since it is so difficult to compare swimmers, eras and medals, we came up with a somewhat mathematical -- but nonetheless, still imperfect -- system to calculate who would make the men's "Greatest Swimmers of All Time" list. Call it swimming's version of March Madness.

As part of our calculations, we looked at number of Olympic golds earned in individual events, as well as silvers and bronzes. We also factored in world medals. World records and relay medals were accounted for as well, although we tried to take into account whether someone earned world records in more than one stroke.

Based on our calculations prior to the World Championships, Spitz held a tenuous hold on the top spot, with 166.5 points (Phelps was No. 2 with 161.5).

After worlds, however ...

Phelps' five individual golds and four individual world records in Melbourne drowned the competition and vaulted him to No. 1 with 214.5 points.

(By the way, Australia's Michael Klim finished fourth based on our calculations, but he still was bounced from the list because he has not won an Olympic gold medal in an individual event.)

So below is our list. Let's chat again next summer.

1. Michael Phelps
What more can be said about this guy? Paul Yetter, who coaches Olympian Katie Hoff, was Bob Bowman's assistant when Phelps trained in Baltimore. Said Yetter: "Michael is a talent not to be seen ever again. Not in our lifetime." Phelps boldly went after Spitz's Olympic record and won six Olympic golds in Athens. He also scored two bronze medals. What we witnessed in Athens and Melbourne is just a scary preview for his competition in Beijing and London.

2. Mark Spitz
If individual Olympic gold was the lone calculation in determining the No. 1 swimmer of all time, then Spitz easily would be No. 1. Not only did he garner seven golds in one non-boycotted Olympic Games, but he set world records in every event. Phelps came awfully close to matching Spitz in Athens, but not close enough. "To me," said Rowdy Gaines, "Mark Spitz is an automatic. He's the greatest swimmer in history. But if Michael just makes the Olympic team in 2008, he'll be the greatest, because if Michael makes the team, he'll win medals."

3. Ian Thorpe
The Thorpedo, who stunned many in the swimming world by retiring at age 24 back in November, will be remembered as one of the greatest freestylers of all time. He also won the 200 free in Athens, which has been dubbed the "Race of the Century." Others in that spotlighted race? Phelps, Grant Hackett and Pieter van den Hoogenband.

4. Grant Hackett
One of the best distance swimmers, Hackett has won two Olympic gold medals in the 1,500 free. In addition, he has earned 17 gold medals at worlds. No other swimmer has more Olympic and world gold medals combined (30 overall; 19 gold, seven silver, four bronze). He failed to medal in the 1,500, however, this past week in Melbourne.

5. Roland Matthes
Considered the top backstroker of his time, Matthes won a total of eight Olympic medals -- four gold -- in two trips to the Olympics in 1968 and 1972. The East German went undefeated in major backstroke competitions between 1967 and 1974. He also set 16 world records.

6. Michael Gross

The West German star, nicknamed "The Albatross" for his wingspan, earned three Olympic gold medals, all in individual butterfly events, in two Olympiads. Overall, he owns six Olympic medals. Olympic champion John Naber once remarked that Gross was a better swimmer than Spitz.

7. Aaron Peirsol

One of the best backstrokers, Peirsol owns four Olympic medals -- three gold and one silver. He is currently the world-record holder in the 100 and 200 back. When he was 15, he became the youngest American to break the 2-minute barrier in the event.

8. Alexander Popov
The Russian captured four Olympic individual gold medals, two apiece in the 50 and 100 free, in 1992 and 1996. His time of 21.64 seconds in the 50 set June 16, 2000 remains a world record.

9. Matt Biondi
The former swimming and water polo star at the University of California at Berkeley, Biondi matched Spitz's record as the second swimmer to win seven medals in one Olympics. He captured five golds in Seoul in 1988 and set world records in four events. He owns the most Olympic medals of any swimmer with 11.

10. Vladimir Salnikov
Many Americans probably don't know much about this guy, largely because they didn't get much of a chance to watch him swim. Salnikov won three gold medals in the American-boycotted 1980 Olympics in Moscow. At those Games, Salnikov became the first man to break 15 minutes in the 1,500. He didn't get a chance to compete four years later, when the Soviets returned America's favor and didn't compete in Los Angeles. What makes this swimmer impressive is he remained on top of his game in 1988, when Salnikov was 28. In Seoul, he won Olympic gold in the 1,500.

Honorable mentions

Pieter van den Hoogenband
A three-time Olympic gold medalist (he won both the 100 and 200 free in 2000 and defended his 100m gold in 2004). His world record in the 100 free (47.84 seconds) set Sept. 19, 2000 in Sydney, still stands. He probably would have won more Olympic gold had he been from the United States or Australia instead of the Netherlands because his relay teams would have been stronger.

Johnny Weissmuller
If you're a swimmer and you've never lost a race, you're pretty darned good. Even though Weissmuller competed in the early days of the sport, he still won five Olympic golds -- three in 1924 and two more in 1928. Later on in life, he became known for more than swimming. He starred as the leading role in "Tarzan" movies. Now that's an unmatchable double.

Don Schollander
He won five Olympic golds in the 1964 Games with individual victories in the 100 and 400 free.

Brendan Hansen
He captured three Olympic medals in the 2004 Games, winning a gold, a silver and a bronze. He also owns seven world medals, five of them gold, and is the world-record holder in the 100 and 200 breaststroke.

Ian Crocker
A four-time Olympic medalist, Crocker won gold, silver and bronze at the 2004 Games. He was a member of the 400 medley relay teams that set world records at both the 2000 and 2004 Olympics. He has been one of the top swimmers to beat Phelps, and won the 100 fly at the 2003 and 2005 worlds.

Gary Hall Jr.
Hall Jr. won five Olympic gold medals and was one of the sport's best sprinters. In three trips to the Olympics, Hall won gold in the 50 free twice and was runner-up to Popov in 1996.

Michael Klim
The Aussie star won two Olympic golds, but both came in relays. Earned 29 medals in Olympic and world competition, tying Hackett for the most all time -- 12 of those medals are gold.

Amy Rosewater, a freelance writer based in Baltimore, is a frequent contributor to ESPN.com.