Original RBA, NOT RDA, but with tank, so RTA....Ok, got it. There is only one choice for those new to the vape world and that is the Kayfun Lite Plus. Since the 3.1 has been discontinued, pending release this Spring of the KF 4.0, that's your only choice, imho. There are some very good RTA's out there, but they vary in degree of difficulty. The KF is easy to build, provides a great vape.....I don't think you can beat kanthal microcoils with cotton in a Kayfun. Some good contenders are the Aqua (much more difficult double coil), the Taifun (really for mesh and/or cotton/silica builds). Some vapers prefer the Genesis style, and the RSST is the go to entry level Genesis, but it's a clone of the Vapinaze AC9 1.3, which has been sold out for some time, and perhaps replaced by the AL1, but I'm not totally sure of that. One vendor, Cloud 9 in England, no longer carries the AC9, but still carries the SvoeMesto Kayfun. Yes, the KFL+ is definitely the way to go. Fabulous vape, relatively easy, lotsa good videos, not ridiculously pricey. My two cents. YMMV. Good luck in your VapeQuest!
BTW, I like the Kayfun's with 28 ga kanthal and cotton wicking. Yummy, around 1.5 Ohms and 9 - 10 watts. Fabulous. Good luck! Ciao.