@ frostedflames:
It's easier when you understand that when you choose one model over another you are basically choosing a battery more that you are choosing a whole system. Here's what I mean:
Say you choose an eGo, here's what you can do with it;
battery + atomizer +cart
battery + t-atomizer + t-cart
battery + 510 cartomizer
battery + eGo cartomizer
battery + clearomizer
battery + LR atomizer + drip tip
battery + atomizer + drip tip
battery + adapter + kr808 cartomizer
battery + 306 atomizer + drip tip
battery + adapter + 901 stuff
basically, the only thing you can't change or add is the battery.
NOW, if you buy the eGo (also the knock off Riva510) then you can use any 510 or eGo stuff with it. BUT, you can use a lot of other stuff with it if you want to because they make adapters for that. So the real question is what kind of battery do you want?