Anything with EL84s. I find they're set up to do the Vox thing, which to my ears only works for singlecoils. Buckers + Vox = thick muddy mess.
I often find that Voxes sound muddy yet too shrill with humbuckers and yet sound fine with single coil guitars.
I have also found issues with some big amps that maybe sound great once you open them up to stage volume (assuming you are playing a big theatre) but you can't use them at home as they sound rotten at low volume.
I liked my Jcm800 2205 split channel though, although my rack through a 10w single ended power amp suits me best - I use an MJW one with my Egnater modular system.