I might buy a new amplifier, and the Vox Valvetronix series is my wise choise. Anywho, I'm still not sure if I should buy the AD30VT or the AD15VT. They are identical in functionality (only the AD30VT has got 'wattage control', dunno what is it, but probably useless) and the AD30VT has a 10 inch speaker, where the AD15VT has a 8 inch one.

I currently have a 15W Marshall MG (solid state) and when playing distorted I set the volume to a maximum of 15% of the total capacity.

Now, my question is, why should I buy the 30W version instead of the ?60,00 cheaper 15W?
the wattage switch means you can turn the 30watt down to like 15 or something like that for playing at lower volumes or to use less power
Will u be taking the amp gigging or is it just a practice amp?
My Gear:

Epi Les Paul Standard
Fender 48th Street Strat
Vox Valvetronix AD50VT
Martin Koa Acoustic
Some crappy unnamed bass
U can lower the power and get better tones at lower volumes with the 30.
But id go with the 15 if u only use the mg at 15%. The 10 inch speaker would give better bass responce than the 8 tho...