I use the Scorpion AGM's from batterystuff.com. So far, very good. I didn't even trickle charge them in the winter.
My buddy must have half a dozen of them in various bikes and he swears by them. He's tried several other brands and they all crapped out. But the Scorpions have been going strong.
The main advantage is that there is no more acid spill and rust on the frame and battery box.
I have two in two of my 550's.
