For the sake of this discussion, lets assume we're talking about on-foot scar-vet only, since you'd be quite foolish to take a great weapon while mounted...
With such precious few magical attacks available to combat oriented lizard armies, I think you'd be nuts not to take magical attacks on a character. But again for the sake of this discussion, I'll also assume you are going to take venom of the firefrog to boost yourself to str7 magical poison attacks. This puts the cost a little less than chotec, and takes magical out of the equation (since both are now magical).
Str7 vs. Str5 (both at -4 to armor)
Well, this would be a no-brainer of course. Higher is better and all. But how much better? When you get down to it, warhammer is predominantly a game with T3 models being the standard. If going against T3, both weapons will do roughly the same damage, with a few freebies from the great weapon's poison. T4 is common, but slightly less so. T5 and up becomes quite uncommon. The only reason exceedingly high strength is valuable (other than the odd chariot pop) is the armor busting capacity, which equals out with these two weapons. The standard heavy armor and shield trooper fighting to the front has 3+ armor, which -4 AS negates perfectly.
Flaming vs. not
Regeneration is becoming popular, and if you have a hero supporting a block of troops (at least, he SHOULD be if he is on foot), what happens when you get hit with a block of regenning troops? The hero with the flaming weapon will swing the tide of battle your way much more reliably by killing off rank and file. Being able to put some wounds on a hydra and striking fear into the hearts of flammable enemies is valuable as well. Flaming takes a few of those "what if" scenarios involving regen off the table.
Defense!
Ok, it is bad enough your scar vet is on foot without the armor bonus from a cold one... now you want to take his shield away too? He just becomes a little too squishy for my taste... T5 with 4+ armor... hmm those are the defenses on a gyrocopter! And that thing always gets blasted to #$@. You could put up with stupidity taking hide of the cold ones, but that's quite a price to pay for something that can be gotten with just riding a cold one (which grants mobility and a few other smaller benefits). A normal scar-vet on foot, I'd want to see carrying an enchanted shield, which is possible with a one-hander like the burning blade. Getting him that 2+ save is enough to start discouraging people allocating a lot of attacks and picking off those two wounds on the scar vet.
Chariots
Really, having a great weapon on your slow ground-pounder of a scar-vet will only give chariots one unit they can't charge to the front. Quite likely, it will just charge something else (or the side of the vet's unit), since it will be faster than M4 anyway. I think of it like the mirror shield... seems really cool to reflect all those missiles but the opponent won't cast at that unit knowing how bad it will go for him. There is of course value in altering the enemy's plan, and if you expect 2 or more chariots it might be worth it... Then again would those chariots really be charging a saurus unit frontally anyway?
So you can guess my vote goes to BBoC, but the great weapon JSoD is still doable, as he's a one man suicide squad anyway. But for all traditional purposes, the BBoC is a great value for its points.
). Although, if on a Cold One I normally take a stock standard spear rather then the burning blade anyway.
