I use a real amp and cab. It's hard to beat it if you have the gear and environment. There really is a life to the sound of a real amp and a mic'ed up cab that is almost impossible to replicate. There's those who say the whole "life" and "air" to real cabs is bullshit, but I think they are just trying to convince themselves that IRs sound the same. Or, maybe they are deaf from years of standing in front of cranked 4x12s. Who knows. I do use a load box from time to time, but that's mostly for scratch tracks or if I'm dialing an amp and I need to hear some fine detail without any bleed from the cab room. If I want a really clean(should I say "sterile"?) modern metal sound, I use a load box. With a good load box and quality IRs, you can absolutely get a great sound. By good load box, I mean don't get a Two Notes. I know this is probably going to piss off the Two Notes fanboys.