"It was an easy decision for me," Tomlin said Tuesday at his weekly news conference. "Obviously, Lacy's a top-quality back, but probably it's a matter of preference -- just like I'm sure Cincinnati went through the same discussions and thoughts when they took Giovani Bernard in front of both of them."
Bell and Lacy will get to showcase their skills opposite one another Sunday when the Steelers visit Lambeau Field.
The second round of this year's draft produced a run on running backs, as five were taken starting with Bernard at No. 37 overall.
The Steelers selected Bell with the 48th pick, and Lacy lasted until near the end of the round, when the Packers took him with the 61st selection.
Tomlin said recently he took responsibility for all of the draft picks that have been made since he became the Steelers' coach in 2007. When asked if he had the final say in draft picks, Tomlin got a tad testy.
"I'm not getting into that," he said. "That's an offseason discussion and really it's irrelevant.
"Regardless of who antes up opinions, they're all Pittsburgh Steelers decisions and we stand collectively behind the decisions that we make as an organization."
Lacy has made the biggest impact of the rookie running backs, as he is seventh in the NFL with 1,028 rushing yards and is averaging 4.1 yards per carry.
Bell is averaging just 3.3 yards per carry, but last Sunday night he joined Franco Harris and Bam Morris as the only rookie running backs in Steelers history to gain at least 1,000 yards from scrimmage.
Bell has 646 rushing yards and 388 receiving yards, and his pass-catching ability is another factor that drew the Steelers to the 6-foot-1, 244-pounder.