Vernon taking Mosely's O and beating him again on the return is better than Thurman's whole resume. As far as stylistically, Vernon had a lot of levels to his game. Thurman not so much. I would confidently pick Forrest to win.
Thurman might have made a good sparring partner for Forrest or Mosley as they trained for each other. He was levels below them.
Well, it's two better than good wins, it's two great wins. And he had quite a few "good" wins on his resume.
I would concur that Thurman's resume might have slightly more depth (It's not that clear cut either, Steve Frank or Santiago Samaniego were solid fighters just like Karass or Bundu) - but @Seamus is correct. When Vernon beat Mosley, Shane was considered PFP top 3 at the very least, in his physical prime, having just recently beaten prime Oscar De La Hoya. That's not just a good win, that's a great win - and He beat him twice.
The fight goes the distance. Forrest has two slightly better wins against Mosley, but he also has losses to Mayorga and Mora. His first loss to Mayorga was embarrassing. Keith was beaten only once by a still dangerous Pacquiao. At their best I still may favor Forrest, but I wouldn't want to put money on this fight either way.
I picked Forrest, but Thurman presents much more of a problem than he's getting credit for. He's remembered for the Manny fight, but he had checked out years earlier despite being relatively young.