Classic 30 or a Blues Jr. would be my choice under $600. You might need to augment with some pedals to get into the metal range, but both are really good amps.

oh really? yeah the Emi in the bandit made a huge difference. It sounds really awesome and I OD it with a vintage tube monster vt-999 pedal with a 12ax7 tube in the pedal gives the bandit a nice tone more than it already had. Then if the classic is gonna sound close to bandit then probably scratch that lol