I use C-E2 XL Carto's. They cost alittle more up front, but can be refilled several times. I use two at a time. I find they're somewhat sensitive to juice viscosity. So, I use two and switch back and forth when I detect a change in the vape. This allows a dwell time for the wick to catch up. These cartos hold 1.7 to 1.8 mL of juice. So two of them lasts me more than my work day and the half hour drive each way to and from. The minor drawback of having to use a syringe to fill them didn't take long for me to get use to. I've been using the two presently attached, one each, to an Riva and an eGo for going on a week. Refilling once a day and that's all the messing around there is to it. Good luck with your quest for your perfect solution.
Cheers,
otrpu