I would say that, unless you can hook up with a group of people who know the caves, a first-timer would be much better off with a guide. This is for a bunch of reasons: Some of the systems are rather hard to find (like NoHoch). In some of them, the main line is very hard to find (like upstream Carwash). Some systems aren't even accessible to anyone but selected guides (like Aktun Koh). Logistics can be challenging, if you don't have good information (like finding the fill station, or figuring out from whom you can rent tanks).
None of these things is difficult, if you go with somebody who knows the area, but I think they'd add up to a lot of frustration and lost time, if you came alone.