If you’re looking at solid state amps, up those numbers a little bit. Solid-state amps are rated by the amount of power they use. Tube amps are rated by the amount of power they use when they begin to distort. And not all amps of the same wattage are equally loud, so these all ballpark estimates).
Next up, do you want a combo or a head/cabinet set? The head/cab set requires more setup, more gear to schlep around, but it also gives you more flexibility and you can play through different speakers – and yes, you will hear a difference.
Combos are generally more mobile. Gigging musicians should consider the possibility of combo amps which allow you to add an extra cab – the difference in your stage presence from a second speaker can be substantial, even without changing your power level.
The next important question is if you are looking for an amp to give you a specific sound, or if you want something that’s highly versatile. If you’re really looking for a signature tone, you probably want a tube amp. More versatility may come with a solid-state or modeling amp, however.
Do you use a lot of pedals? In that case, you probably want an amp with an effects loop – but you probably don’t need a two-channel amp. If you don’t want to have a big pedalboard, a two-channel amp is more important. Ask yourself how important are built-in effects like reverb or a tremolo?
When you go to a guitar store to check out the possibilities, bring your guitar, or, at least, play with one of theirs that’s the same make and model as yours. Guitar and pickup type, of course, makes a huge difference, and you want to know how it’s going to sound with your rig.
You will help the salesman help you if you can succinctly define the styles you’re likely to be playing, as well as naming one or two guitarists who inspire you, who you’d like to emulate. The salesman will steer you differently if you say Slash compared to Stevie Ray Vaughn or Kirk Hammett.
Don’t be rushed. You don’t have to buy the first time you go into the store. This is especially true if you want to check out some guitar amps that they don’t sell. Go ahead and tell the salesman you want to go check out some other models, and that you’ll be back.
(By the way – I strongly encourage you to buy local – there are lots of advantages. But that doesn’t mean you can’t go to thefistfam.com or another online retailer and check out the online price. There’s a good chance your local dealer will match it, and he might even cover the sales tax.)