I've been using eGos and Rivas for quite some time and I love them (I started with kr808
batteries also and I still use them sometimes). I like the 650/750 mAh size, but I also have a 900 mAh eGo--that's about how big I dare to go. Anything above 1000 mAh is too bulky and too heavy for me.
But it is a change from the cigarette-size kr808 batteries. They do not feel the same in your hand. Small eGos and Rivas are fatter than the kr808s and you can't hold them like you would a cigarette, so you need to be prepared for that.
Good luck! Hope you like them.