Jeff Bagwell and Frank Thomas are inexorably linked. They were the preeminent first baseman in the 90's, both winning the MVP in 1994. More than that, though, they share a birthday, both born on May 27, 1968. Because of his connection to Bagwell, Thomas was my favorite American League player in the 90's.
The general consensus I'm seeing is that Frank Thomas is likely to be inducted in his first year of eligibility, and will almost certainly receive more votes than his birthday mate. He's already got one more vote, as Bob Sansavere dropped Bagwell in favor of Thomas on his ballot this year. Here's the thing, though. Bagwell was better. There should be no reason to check the box next to Frank Thomas's name without also checking Bagwell's*
Thomas was probably marginally better than Bagwell on offense, but its much closer than it might look at first glance. Thomas ended up with more counting stats, largely because he played three more seasons after Bagwell retired at 37. However, they were very close through age 37. In fact, following their age 37 season, Bagwell has 449 HR compared with Thomas's 448, and led the RBI count 1,529 to 1,465. Of course, Thomas was very good in his age 38 season, and not awful at 39, so of course he gets credit for that. Thomas also has slight leads in all the rate stats, with a .301/.419/.555 line compared with Bagwell's 297/.408/.540. Thomas's career 154 wRC+ ranks 21st all time. Bagwell's 149 ranks 30th. While Thomas was slightly better on offense than Bagwell, both rank among the all time greats.
And that's where it ends with Thomas. Thomas was a first basemen in his MVP years, but very quickly switched to the DH position. He did not start over 100 games at 1st after 1996. In total he was a first baseman in only 971 of the 2322 games he played. And he wasn't exactly a gold glover at first when he was there. In fact, Fangraphs ranks Frank Thomas as the worst defensive first baseman of all time, by a fairly wide margin. He was also poor on the basepaths, accumulating -34.7 runs.
In contrast, Jeff Bagwell was a good fielding first baseman, winning the gold glove in 1994 (and possibly even deserving it), and was a net positive on the basepaths as well. He twice stole 30 bases in a season, and ended up with 202 total, against only 78 caught, for a 72% success rate.
Add it all up, and you get a picture of a one-dimensional offensive force versus a true 5 tool player. WAR agrees, as both Fangraphs and Baseball Reference have Bagwell in the lead. A vote for Thomas and not Bagwell is a vote that defense and baserunning do not matter at all (shades of the Trout/Cabrera debate, which does not bode well). I personally believe that both are clear, no doubt Hall of Famers, and I hope Thomas gets in. But there should be no reason why Bagwell should not share in that honor.
* This article willfully ignores the elephant in the room. This article also thinks that elephant in the room is a big stupid hypocrite, and deserves to be ignored.