Well, first of all, wattage is much different in a tube amp. You could take a 50 watt full tube amp (say a Fender Vibrolux) and it would blow a 100 watt solid state amp (say and Ultimate Chorus) out of the water. I have a Fender Hot Rod Deluxe 4x10 and it's "frickin'" loud (60 watt). Bang for the buck....
I'd go with a 15 to 30 watt full tube amp (trust me...they get really loud and awesome tone). Try the Fender Blues Jr. 1 12" speaker, full tube, reverb, and tone that will make you cry.
Tube amps sound better the louder they get. The advantage of a low watt full tube amp is...you can get that sweet tube tone and have you amp at a tollerable volume at the same time.
Try them out...go to a store and crank it...pretty cool.
Oh, PS...what type of music will you be playing...I guess that should have been the first question.