I would pick Lashley for this fight, here is why...
The obvious victor if these guys stand and trade blows is Kimbo. Lashley obviously wouldn't do that... I think he'd do very similar to what Lesnar did, and thats shoot and takedown straight away. The trouble with Lesnar was... he was against Frank Mir who is a great Jiu Jitsu heavyweight - Kimbo is not. Kimbo won't knock Lashley out because Lashley won't stand with him, and if he wants to take Kimbo down, I don't think he would have a problem in doing so.
Kimbo will always be good against guys like Bo Cantrell and Tank who are going to stand and bang, thats what Kimbo is, thats his roots.
Fedor fights I want to see..
Fedor vs. Josh Barnett
Fedor vs. Randy Couture
Fedor vs. Tim Sylvia -
Fedor vs. Andrei Arlovski -
hmmmmm, i wonder how many become reality..