At this point in time, it's like taking a couple of turds and asking which one of them stinks less. One turd might be bigger than the other but, when it's all said and done, they're both still turds.
If these two were in WWE with the same sort of character, people would be labeling these guys as a couple of generic, one dimensional meat bricks getting pushed because Vince loves their look. And those people would be absolutely right. However, that seems to be perfectly acceptable since they're in TNA and are already being touted and debated as the future of the company.
When it comes to Gunner, there's just nothing to be said. He's spent his entire time in TNA playing the role of a generic lackey & general stooge in Immortal that just happens to have a good muscular build and some tattoos. And all this "intensity" in him amounts to little more than him making some angwy wangwy faces while slapping himself. Everything about the guy screams generic mid-card place holder.
As far as Crimson goes, I just see a big guy with a good look that TNA is pushing and pushing hard. Right now, he just comes across as a poor man's Goldberg. Yes, yes I know that TNA isn't doing the exact same thing WCW did with Goldberg but there's more than enough similarities to warrant comparison of the two. As far as intensity goes, same with Gunner. He makes some faces, maybe snarls or something a little and that's about it.
So who's better?

Crap by any other name still draws flies.