if you're not too sure yet i'd recommend an IGO W or an IGO L. The W is for dual coils & the L is mainly a single coil job.
These are good & they are cheap but tried & trusted. If you're going to be experimenting with coils & adding wear & tear to a device then these are a good place to start.
The more expensive rda's, higher end jobs are a mixed bag & all have their own character, it's easy to spend a lot & then find it's not your device like but the UD IGO drippers are good.
The W is a standard 3 post linear job with post holes & screws for clamping & dead easy to build into.
The L lacks the post holes & so you have to wrap the wire around the screw.
Both good methods. The only drawback with these is that they are issued with pretty small air holes in the top caps. It's ok but makes for a tight draw & a lot of vapers do drill them out a bit. I have a W & it was about 3/4mm standard, i drilled the holes out to 2x 1.5mm & now it gives a good flavour, not the best but that's ok, not everything has to be.
There's the IGO T...
I think the T (Titanium) is a good one with its reduced chamber & gives a nice vape.
There are other IGOs as well but those more basic ones remain a good solid standard i reckon.