Do you want a tube, or a box? Do you want a bottom feeder or will you be using standard atties and/or cartos/
tanks or RBA/RDA's? Do you want VV or VW or do you prefer mechanicals? What size batteries do you prefer? I have had a bunch of them, but the most readily available one that I personally love is a REO Grand, it is a mechanical 18650 bottom feeder. But everyone has different needs, budgets, etc.
If you want a tube, of course the ProVari is always a good buy because of its durability. If that is too steep, I prefer the Vamo because of the menu options with the buttons.
Good luck finding something you love!