Personally, 6550's are killer tubes, but that's my personal preference. All aspects of tone are according to the eye of the beholder, so if you like what you have, stick with it. If you want something a little more particular, figure out the best description(i.e. dark, bright, doom-y, bluesy, etc.) and it may give people something more to work with. List off what style(s) of music you'll be playing through the amp, what levels you'll be playing at(I believe the SS rectifier outputs more than a tube rectifier, but I could be wrong -- corrections anyone?).
Otherwise, if you do a few quick searches on here, you'll find pretty much everything you may want to know. If you find something close to what you're wondering, you can always trying sending a PM to the person who posted said information. They may be able to offer advice specific to your needs.
Good luck!
XXX