I'm a bit biased towards top AF due to hating any leaking whatsoever. But that being said, top AF RTAs have come a long way and give a great vape now. My favorite is the Zeus single for it's top airflow, easy filling with the 1/4 turn top fill, and the easiest to wick. Plus the tank can be 3/4 full and can be removed to re-wick with out spilling (you need to disassemble and reassemble upside down, obviously, but very easy to do).
For wicking, it looks a bit strange at first to lay the wick a bit to the side of the coil to lay it in the juice channels, but it so open it's really easy. Just a thin line of juice on the wick and let is saturate for 5 seconds and lay it in the channel. I use rayon, but if using cotton wait 15 to 20 seconds to saturate before laying in the channel. But the best part for me is that I don't need to guess at the wick length and cut first. Just leave the wick long and after laying in the juice channel just snip it off at the juice channel base. It's so wide open and easy to get to with a small scissors it's the easiest way to get perfect length every time. I don't like faffing about with wicks, so this is a big plus for me. Quick, easy, and effective.
Honarable mention goes to the Augvape Intake. Another of my favorite single coil RTAs. Reasonably easy to coil and wick, no leaking, easy fill, inexpensive, and good flavor. All around a good vape.
I've got more than a few RTAs, but not as many as some on the forum, but these 2 are inexpensive, easy to work with, and give a very good vape.