I know there are ESP-01, ESP-07, ESP-08, ESP-12 modules for example (now ESP-14 too??) and I see variations on sale on eBay and AliExpress but I don't know the difference between them.
Many of my projects only need limited capability but I've been buying ESP-12F modules so far - if some of the older modules can do the job then I'd happily use them.
Cheers,
Brian