ZZ-OP (OCLL->PLL) is where every ZZ user should start. It is only 28 algs, and you likely know them all already. These algs apply to pretty much every ZZ variant, so there's nothing to lose starting here. Also, despite being very few algs, it's pretty fast.
ZZ-VH (COLL->EPLL) is overrated. I don't think it's worth using tbh. OCLL/PLL is faster on average. Just skip straight to learning basic ZBLL.
ZZ-A (ZBLL) is currently the fastest variant. Most ZZ users only learn a small chunk of ZBLL, and use OP for cases they haven't learned.
ZZ-B (phasing->ZZLL) is an interesting variant that
@OreKehStrah says is a good stepping stone towards ZZ-A. I haven't really explored it much, so I can't say much about it.
OK now ZZ-C family!!
ZZ-C (OCLS->PLL). Lots of good cases worth learning here; but it's a lot of algs, and a lot of the time CT or HW is better because the TSLE or WSLC alg is shorter.
ZZ-CT (TSLE->TTLL). Swag variant. Algs are currently being developed.
ZZ-HW (WSLC->WDLL). Swag variant. Algs are highly undeveloped, as the variant was very recently rediscovered by me. I am currently developing the algs (which is why the D is in WDLL), and they are very promising. Check out my ZZ sheet to see the WIP WSLC and WDLL algs.
Now ZZ-D (CPLS->2GLL). I don't have much to say about it. it's a solid variant. Good for OH. I personally don't like CPLS recog, but that's just a me problem.
I don't know much about other variants that haven't been explored much.
I personally plan to do ZZ-C CT HW option select.