You'll get a wide range of recommendations, I would guess, depending upon different people's experiences. This question is a lot like asking what the best car is to
buy -- it depends upon what your expectations and budget are.
- Are you a mouth-to-lung (tighter draw) or direct-lung (looser draw) inhaler?
- Flavor chaser or cloud chaser?
- Top or bottom fill tank preference?
A lot of old-timers will probably mention one of the Kayfun-style tanks. I have experience with the Kayfun Lite Plus which is a classic mouth-to-lung flavor-chaser tank. It suited my needs for over a year, but my vaping preference has changed to a more open lung draw so it rarely gets used any longer.
Other old-timers will mention a Genesis-style tank. I have experience with these, too, but I don't like using stainless steel mesh as wick, and they are not great out-and-about tanks in my opinion.
I don't have any experience with any of the more recent RTA's.