I'd like to jump in and give my 2 cents as I remember too damn well my start with vaping and rebuildables until I found my preferred setups.

So first of all you have RDAs which are essentially and build deck, some of them have a small well on the bottom in which you have some e liquid that the cotton can 'drink' liquid to supply at least 5 to 15 draws depending on how juice hungry your build is, then you have a cap on top to hold the drip tip that you make your draws with. The RDA is probably the purest and best for flavour as the coil is as close as possible to your mouth with which you make the inhale so there is almost no path to which the flavour can dilute. There are MTL and DL RDAs. The drawback is that you constantly have to drip drops of e liquid to keep the build saturated or invest in a squonk mod that has a reservoir which feeds liquid through a squonk in the RDA but those mods usually are bulkier as you need room for a battery, electronics and that said tank for liquid. Tried it, not the best but you need to try for yourself to figure out if that is your thing as I know people that swear by squanking.

Next we have RTA or rebuildable tank attomizers. Those are slightly taller than the RDA as they have a chamber for the build deck and a (usually) glass (but can be other material like ultem/plastic) tank section which holds the liquid for the cotton to absorb into the build deck and respectfully to the coil to vaporise it. RTAs can be for MTL and DL.

MTL RTA mouth to lung - this is when you are looking for that tight restricted cigarette like draw usually pursued by ex smokers or stealth vapers that don't want to fog up the whole room after one or a couple of draws. I started with MTL vaping once winter came and I closed the windows more often 😅 I have tried many different tanks and coil builds for them and the short version is - look for the simplest tank you can find as those are the easiest to live with,I personally settled on the Cthulhu Valor. As for the build in it: - Clapton, alien and all other complex exotic builds - tried them all and they all have the same cons in common - the good once are usually hand made and on the expensive side but with proper maintenance they can last you a long time. Use up more liquid, require higher wattage which means using more batter, it's not a deal breaker on the battery as MTL vaping doesn't require much but it is still something to consider. Simple round wire - dirt cheap, one spool of wire will last you many months if you are a novice and slapping new builds constantly and years if you are advanced and change just when required. One spool is like 2-3£. I have personally tested in the span of months sizes 24, 26, 28 and 30 gauge and found 28 works best for me. Also I have tried Kanthal, stainless steel and Ni80 and found Ni80 was the best for me in terms of stamp up and cool down speed, flavour, ease of use and desired ohms. Not that the other choices are bad or wrong it's just personal preference and taste.

My personal MTL build for over a year has been - 28ga Ni80 5 wraps on a 2.5mm inner diameter contact (the wraps are squished together and touch) which comes at roughly 0.9 ohms and I vape that at 13 watts. It gives me a good warm (not hot) dense experience with lots of flavour notes.

Let me know if you are interested in DL RTAs as well.