For single coil my top recommendation would be the Citadel from Psyclone Mods. Easy to build and fantastic flavor. They shut their doors but you should be able to find it. The Claymore is a good cheaper option that also has great flavor. Also the KRMA from Mission XV, fantastic little RDA that is on sale now from the manufacturer. Comes with two top caps. Also the Entheon/Hadeon from Psyclone is awesome, get the version with both caps as the Hadeon cap is the better one. If you get the Claymore, I advice you to get a better drip tip, the ones in the box are either uncomfortable or restricted.
I don't use dual coil very much, but the Asgard mini is phenomenal, as are An RDA For
vaping (yes, that's what it's called), and the Nightmare 25mm - all good. Also from Vaperz Cloud the Temple 2020 edition in either 25 or 28mm. The 25mm is best suited for 2.5mm
coils, the 28mm is more roomy.
For squonkers the Topside dual from Dovpo is the best dual battery option available, for single cell the Eleaf Pico Squeeze 2 and Vandy Vape Pulse v2 are good, the Dotmod Dotsquonk 100w is fantastic. There are tons of good mech squonks, like the SQ217 from Signature Tips. If you go single battery I recommend going 21700, Molicel P42A are good, Samsung 30T also, a bit higher CDR but lower mah rating.
If you have any questions, just ask
EDIT: If you don't have a vape toolkit, I'd recommend the one from Wotofo. IMO the tools are higher quality than the ones in the Coilmaster kit, especially the snips (they are also sold separately). It does not come with a coil jig, but two stepped coil rods.