the other guitarist in the band has just ordered a tsl100 and claims that if i don't get an amp with around the same wattage it woun't sound as "big".
......
For the same price (£600) i can get the orange rocker30 (30 watts) and claims to be pretty hi-gain. but 1) will it be loud enough? and 2) will it sound "big" enough?
Don't listen to the other guitarist, and don't confuse 'volume' with 'spread'.
Sure, a 50w marshall and a 100w marshall might have different tonal characteristics, but you'll never get either of them running full tilt (without breaking windows), and you'll struggle to hear a volume difference between them.
In my opinion, a 30w head running through a 4x12 can sound much bigger than a 100w head running through a smaller cab. Remember also, that the magic happens with valve amps when you get the power valves really working. This happens when you wind the volume up.....somthing which is marginally easier to do with a lower wattage amp.
Just my opinions....