It really depends on vaping style. I tend towards the care free style(drip through the tip). I would not suggest bottom air flow for this style, I have a freak show and leak allot.
If you paint your coils, then bottom air flow is fine.
I try to find an rta that compares to an rda for even more care free vaping, but nothing compares to rda....goblin mini is close.
For care free dripping I'd suggest sapor then, velocity. Velocity isn't as warm and side air flow, but nice juice well.
All said, I've been using my sapor exclusively since I've got it. Derringer is slightly better flavor and warmth, but sapor is just easy.
Plenty here have more experience than me, but i have omega, mutation v1 and v2, doge 2, tobh, hastur, derringer, mephisto v1, zenith, freakshow, magma, cats, plume veil, and veritas.
I like flavorful warm vape, been meaning to go back to the derringer to compare,(I think it is a bit more flavorful and warm)but the sapor is just so easy as far as not leaking and wide bore tip to drip through, that i haven't got around to it.
Velocity is great to build on, sapor pretty easy, derringer is a slight pain. Ideally i am looking for an rda with sapor style tip and airflow, with velocity posts and a more reduced air chamber.