Well, I use an Ego-T, with a 510-808 adapter, so I can keep using the Cig2O cartridges.
You can, in fact, refill the Cig2O cartridges.
What kind of flavor are you looking for? Tobacco? Menthol? Fruit?
For me ? Tobacco of course. As far as nicotine content goes however, the lower the better, since I don;t have a nicotine addiction and I don;t really want to develop one.
I keep my 2 feet on the ground, and my head in the twilight zone.