A small cig-a-like battery that performs well, runs on an auto switch,etc is the holy grail for me
The deal breaker for me, the reason why I reach for the Provari and Reo day to day isn't the battery life, its the atomizer options. I just can't go back to CE2s, cartos, etc. I try quite often, because I love the auto stick batts, but I always end up agitated.
If your favorite atties are small and slim, then Halo, Volt and Bloog are excellent batts. If you want to go slightly hotter go for V4L (unregulated 3.7 vs. regulated 3.7 from the former three)