Stay away from anything sold in the stores. If you want to know, ask the clerk who sells them. It's funny the responses you get.
the two models you want to try are the 510 and the Kr808d-1.
For cig styles, aka analog style, aka slim style pvs, the 510 models aren't that powerful but offer more options to upgrade with.
The Kr808-d models are stonger pv style and do a better job simulating a cigarette but are only now catching up to the 510 as far as upgrade ability to a longer lasting battery. Typical vendors on the forums that are popular in the kr808d-1 style e-cig are Bloog, Smokeless Image, and V4l (vapor for life)
The batteries provide 1-3 hours of vaping and for days you are finding yourself needing to vape more you are going to need extra batteries or a pcc (personal charging case)
If you are a heavy smoker and smoke a pack or more a day you may want to look into a bigger battery. Typical bigger batteries allow you to fill your cartomizers at night and vape most of the day without having to worry about being near a charger or carrying extra batteries.
The Ego/the Riva/the Kgo and the Echo are all great options. Good luck!
-and you can typically get a good larger battery kit for less than those cheap toys you find in the store.