Best flavor in an RTA IMO? Merlin for a single coil build. Dual gets a little harder for me to pick, OBS Engine excellent (and my current all around favorite RTA), Tornado nano is a sleeper but great flavor, Limitless+ can give good flavor with the right build and airflow, and a Boreas can do quite well.
Edit: Oops missed the 30 mm preference. I don't have any 30 mm. Based only on reading maybe a ModFather or the new Aromamizer Supreme 30 mm.