They all sound very similar....I've had all three (in one form or another) and there isn't much difference in volume, but there is more head-room the higher the wattage is. The Single is going to get in to power tube saturation long berfore a Dual or Triple, which also makes the cleans break up sooner. The main difference is the single only has a solid state rectifier whereas the dual and triple have solid state and tube rectifiers you can choose from.
I actually liked my Single recto (rectoverb) better for distortion than my triple but I liked my dual better for cleans (the tirple sounded the same as the dual to me on cleans).
If you get a Dual, you can always pull 2 power tubes and a rectifier tube and run at 50wts too. I did that with one of my T-verbs.
They're all great amps, and if you have a little extra or can save and wait a little longer the Roadster or Road King would be the amp to get!! But if you don't want or need the extra stuff they offer, my vote goes for the dual or single.....The triple is overkill IMO, but there are some that love it.