This is how I see it.
1) A guitar tone is good when it fits the genre but is not generic nor safe but original. So IMO you can't say that f.ex. Metallica has "the best guitar tone". That tone would suck in any other genre. So genre is important. That was my point about using TS + 5150 + Recto cab. It's an amazing tone but it can't be everyones tone. It gets really boring listening to some core bands with almost identical guitar sounds.
2) Most metal guitarists will have too much gain. Don't expect to sound tight if your tone isn't tight. Lower that gain to sound more impressive. Too little gain will sound unballsy. Turn up the gain until you hear your low end disappear and bring it back some.
3) EQ balance is important. If you want a loud mix then your guitar tone should be FLAT. If you want a dynamic mix you can have more low end.
4) Guitar tone is mostly in the guitar players fingers. Learn to play before you even think about amps or cabs.
5) Guitars should not be the focus of the mix. Kick, snare and vocals are the most imporant. A good guitar doesn't necessarily sound good by itself and SHOULD NOT BE POST PROCESSED SOLOED. Post process to fit it in the mix.
Guitar tone:
1) should fit genre
2) has the right amount of gain
3) is balanced
4) is in the fingers
5) should not be the focus of the mix
Now bash away.
That just about sums it up.
Nah.. just kidding. I'm very confident using TH2 and Axe-Fx.