Before we get into RDA discussion, let me throw this out there...
http://vapingunderground.com/thread...-sick-clouds-bro-thread-sticky-edition.78126/
That's my big beginner thread for all sorts of stuff you need to consider, like battery safety, building to your battery's amperage limit, etc. I assume you're familiar with ohm's law, you've got a standalone ohm checker (or you'll be getting one), and you've got an idea what kind of wire you want to build with? If not, please spend some time with that link.
Also, you'll notice I suggest you consider a little about what you want, do some research, and ask questions once you've found a few RDAs you're interested in and want comparisons - I learned the hard way that just asking "What RDA should I get?" even if I laid out very specific goals, tends to result in people ignoring what you want to do and telling you that whatever RDA they bought most recently is the best because they bought it and if they bought it then it must be the best. Even if there's someone out there capable of giving advice on even a quarter of the literally hundreds of choices on the market right now, they're probably busy posting reviews to help you decide on your own rather than waiting for someone to post a thread where they can write a book about all of the different devices they've used.
That said, the Velocity style seems to be quite popular these days - I just received a handful of Velocity clones the other day and I'm running a pair of 0.4 ohm fused claptons with a 3 mm id, 2 x 26g with 38g wrap. Vapes great - this RDA brought me back to dripping after I'd been all about tanks for the last month or so...