I truly believe what is said in the above post: a very large portion of your sound is in you - you're style and how you play. Yes, of course the amp also plays a large part in this, but there are so many other variables such as the bass, strings, bridge, neck, cable, etc. that can also change the sound's character. For example, I play through a Crate BX-100, which is generally regarded as a low-end, cheapo amp. Yet I get the tone I want: how? Is it the bass, the cable, my strings, my style, what? I like to think that I can keep the tone that defines me no matter what I'm playing through - sure, I like some brands better than others (Eden and SWR come to mind), but there are a lot of other good products out there. Peavey comes to mind as one of the brands that I personally don't like at all, yet I've heard a large number of players who sound great through them. Peavey just doesn't work for my setup.
The summary: play through whatever works best for you. Don't play a brand because it's "cool" or "hip". Most of the people that I've met get the sound they want no matter what they're playing through (sure, some people always are in search of their sound, but that's another topic...). And yes, there's gonna be tonal differences, but they won't hold the same for all players.