Well since the swappable RBA kit for the Subtank is a new concept, I can only stick with RDA's and RTA's. My very first was a Patriot RDA. It was pretty good for a beginner. 3 post design and a lot of building area. Airflow was tight, so drilled that out, and flavor was average. As for my first RTA, it was a KFL+V2 and it was great but also a pain. The flavor was awesome, and it was super easy to build, but I wanted to vape at greater than 20W and it just wouldn't work on there lol.
Now I'm on the Magma RDA and Lemo II RTA.
It's bliss.