Go try a bunch of them out in your local store, don't underestimate 2nd hand old amps either! They may not look shiny and new, but some of them have that "magic" quality about them. Find the one you like most tone wise, even if it doesn't have insane high gain in it. You can always find a way round that with a
distortion pedal, or some modification to the amp (like building in fx loops).
As far as the 50w vs 100w argument goes, it basically boils down to this: a 100w amp is loud, but so is a 50w, except to get the 100w amp in that nice region of
power tube saturation you need to play it very loudly. Both versions will have the same preamp though, so your only considerartion is how much power you'll need. Basically 100w is nice and will give you a nice amount of headroom, but will take more volume to overdrive the power stage. a 50w will hit the power tube saturation faster, but will have less headroom. And you can always get a set of earplugs....