That's a tough question and there really isn't a 'simple' answer. Both men are physically imposing figures, Lesnar is 31 years old and is 6'3 1/2" and weighs 265 lbs of stocky farm boy muscle. While Lashley is 32 years old and is 6'3" and 250 lbs of chiseled muscle.
I think that because Lesnar has been training in MMA for the last several years before he got into UFC that gives Brock Lesnar the experience advantage (not to mention having the opportunity to go toe to toe with Randy Coture). Brock Lesnar also has the speed advantage, his muscles are leaner and appear slightly smaller than Lashley's.
Because Lashley is so chiseled this leads me to believe that he might be slightly stronger than Brock, but I seriously doubt that it is a huge strength advantage by any stretch of the imagination.
Brock Lesnar is known for having an incredible 81" reach, that's one thing that Randy Coture cited in an interview after his fight that he didn't expect and plan for was Brock Lesnar's reach, which is a huge advantage for Lesnar that no fighter can train to have, you either have it or you don't.
Brock Lesnar was my favorite WWE performer of ALL TIME and while I appreciate the similarities to Lesnar that Lashley brings, I believe that if they faced off in the octagon Brock Lesnar would beat Bobby Lashley using his experience, reach and speed advantages.
Paul Heyman for those of you who dont know him is the founder of the wrestling company ECW, a former creative team member of WWE who worked closely with Brock Lesnar, and later in the WWE's developmental territory with Bobby Lashley writes a blog on the british news paper website The Sun. He wrote an article about the prospect of Lesnar VS Lashley in the octagon and Ive given the link below.
brock lesnar would kick bobby lashleys ass. not to be racist but black people just swing. and brock will take his time and catch bobby in the face with his incredible 81 reach. and brock lesnar is stronger. it just seems like bobby is more ripped but brock is only half of an inch taller and weighs 15 lb's more. which makes him a pure bull.
okay i realize these posts are old but most of you dont know what your talking about. Bobbys reach is 80 " and lesnar's is 81". But lesnar's shoulders are wider so he has slightly less reach because bobby has longer arms. Lesnar is stronger and faster than lashey. lashely just looks a lot more ripped. But its show muscle, lesnar has functional muscle. Lesnar is more skilled, experienced plus the things I mentioned above. Bobby fights wash outs and lesnar fights top contenders. Although the UFC's heavyweight division is a little stale. Randy is due to start receiving social security in a few years, nog is over the hill, mir should just go home, Shane Carwin is past his prime, and Cain Velasquez isnt a threat. I watched a video where mexicans talked about how proud they were to finally have a heavyweight, too bad he doesnt stand a chance against someone the likes of lesnar. And to fedor fans, fedor beat nog, mir beat nog, lesnar beat mir. I think that fedor is one of the most skilled fighters on the planet but Lesnar has physical gifts. He is just too much for the last emperor. At present no one can beat lesnar. We will have to wait for some monster to come along or for lesnar's strength to fade.