Unless you're playing a pink Samick knock-off from Mexico with flowers and hearts on it - I don't think you have much to worry about in the BM scene.
Here's what to look for as far as what kind of sound you want:
Body wood/Neck wood - different body and neck woods will make a difference in the base sound and tone of a guitar
Pickups - this is obvious - shitty pickups sound like ass
What you're playing it through (pedals and amp) - obvious again
If the guitar is quality in the top 2 categories, and you have a setup as far as pedals and amps that is somewhat in-line with a BM sound - you can pretty much buy what you want. Of course - you may want an evil lookig rig, so that's another consideration. I would put sound and playability first, and looks second.
I just bought a Jackson SLSMG Soloist, and this thing fucking screams. I don't play BM, but I am a big thrash head, and it works great for me. I'll bet with the right pedals or fucking with the one I have, I could get a great BM sound.