If you're not enjoying refilling all the time, you don't want Cartomizers (unless you're getting a carto-tank set, but that's a whole different beast). The eGo-T is a pretty solid design, and you won't have to refill it all the time. When I was using my eGo-T as my all-day PV, I would have to top off tanks at the end of the day, and that was about it. I had about 3-4 of them in rotation.
I use cartomizers right now, and I get the pleasure of refilling them three-four times a day. Fun stuff!
Anyhow, as far as eGo batteries go, you've really got 3 options. The 650mAh, the 1000mAh, and the VV one. The VV is pretty new to the market, I'm not really sure how well it works, or how long it lasts.
I started with a 650mAh, one fully charged battery would last me like 6-8 hours, then I would pop the other one on, and it would last until the first was done charging. I did end up buying a 1000mAh battery also, but I only used it at home, and only managed to empty it if I didn't charge it for a few days.
Hope this helps!
-X
Edit: The E-Power is a good solid device too, but I would really recommend that you find yourself a Starter-Kit to get, especially if you want to go with the tanks. That way you don't accidentally get the wrong parts and have to wait longer.