Temp or wattage simply depends on your coil material- kanthal & nichrome for watts only, nickel for temp only, stainless steel does both.
I am still confused about what differentiates an RDTA from an RTA, but it seems like RDTA has the deck above the tank & an RTA has the deck inside a chimney which sits within the tank. Using this understanding, I personally prefer RDTA because the coils are usually closer to your mouth, delivering RDA-type flavor. You can also keep an eye on your coils & cotton and change out your cotton & dry burn the gunk off your coils without disassembling the unit or removing it from the mod, although it can be tricky to dangle the wick ends through the wicking holes.
If you're planning to be putting it in your pocket or jostling it about, RTA is probably better to avoid leaking out the top, but if you can keep it upright, RDTA is no problem.
Easy enough to change the wick on your RTA by closing AFC & JFC, inverting it and unscrewing the tank (even with a bit of liquid in it) but it always makes me uneasy- I have an Engine mini which tends to seep e-liquid into the air chamber.
Best flavor is RDA and if you get a squonk setup it's the best of both worlds.
Advice for newbies: try all new atties on a mod that has no board (unregulated), or one where the board is placed opposite the 510 connector (like the Livepor Yosta or any squonk mod). I am having an awful time with a Kylin POS that leaks through the 510 pin, which I beta tested on my Yosta. All I had to worry about was sticky batteries instead of a burnt-out mod board.