There are a TON of options. The problem is selection one, or even two. They gave you some good ones above. I can only give you a brief story/journey as a quick answer.
I started with a TRIO. It was OK, since I picked it up locally to "try e-cigs". Helped me decide to quit, find ECF, and move to 510's. Got REAL TIRED of charging batteries. Also explored mods and modding since I had a soldering iron and the inclination. Went to all kinds of 3.7 volt stuff, mostly with replaceable 14500 batteries (highly recommended). Vaping was great. Using atties and dripping. Still not 100% happy tho, but quit nonetheless and stayed off the cigs.
So I decided to try a 5 volt Passthrough. Loved it. Loved 5 volts. Built a 5v box mod. It was great, and portable. 2 AA sized 14500 batteries in a 3xAA box, with atomizer sticking out the top. DIY stuff. There are other ways, vv models, etc. But you get the idea.
Anyway, the bottom line is that you have to have enough "oomph" or you keep thinking about cigs. I theorize that full flavored former-smokers experience this the most. Just not enough oomph. So there's a couple of ways to go about "oomph"
1) use the 3.x volt stuff, and Low Resistance atomizers/cartos. Now, I don't usually suggest anything below 2.0 ohms, and the 1.5 ohm atties have been known to fry eGo type batteries and are a bit too hot for most true 3.7 volt stuff
2) Go 5 volts (or vv even better).
I use option 2 (5 volt mods). I hardly ever think about cigs. It is a cig-like hit, warmer vapor, no long-drag crap, and no stress on the device because it is designed for "oomph". You don't have to make any of them (unless you want to).. there are many 5 volt and vv mods available, along with the "off the shelf" 3.x volt stuff, in many price ranges.
Keeps me off cigs.
Hope you find what works for you!