it also depends on the type of user you are. think about it. a bfg comes factory oc'd and with a lifetime warranty, but that means NOTHING if you're going to oc yourself. a factory oc doesn't mean you get to push it any further, since its still going to be using the same gpu and memory as other 6800gts. after you've oced that lifetime warranty goes bye bye.
with evga you're going to spend 40 bucks less for the same card. if you want to run at the same oc'd speeds as the bfg then go for it, but thats rather stupid considering you can definitely go higher. a 1+1 warranty is nothing to scoff at, neither is the stepup program.
it's your choice really but i feel that a factory oc means squat and a 2 year warranty is nice enough. even if you dont oc and keep everything at factory settings (weirdo), i still think its a tossup between the two. it's your money.