I've had the same question recently. The recommendations I'm seeing consistently around the Yucatán cave diving world are Protec in Tulum and Natalie Gibb with Under the Jungle in Playa del Carmen.
In my opinion Third Dimension is the best in the area due to the multiple agencies the owner (Kelvin Davidson) is an instructor and Instructor trainer for. Kelvin can teach GUE, IANTD, TDI, and NSS-CDS courses. He has tons of experience in OW tech diving (he ran a land based operation in Truk for many years) and cave diving (he's been in Tulum for many years). He and his two other instructors take their GUE training and integrate it into classes they teach for other agencies. They also teach in bm or sm.
Protec is who I used for years, but the quality of customer service dwindle some and we had a bad experience with Rob Bartlett who is associated with Protec Playa. I'm pretty vocal about people avoiding Rob. He's got a bit of an attitude issue and a big head. He's well loved by some, but unless you're giving him your money he can be an ass.
I've never heard a bad thing about Natalie at Under the Jungle. I prefer to be in Tulum rather than closer to where UTJ is, so haven't really used them.
I forgot about mentioning Jon Kieren and Roger Williams. Both have tons of experience, but are newer to Mexico than some of the other instructors. They both have extensive Florida experience, so they can give you insight on the differences between FL and MX cave diving. Jon is a fundies instructor so can bring some of the GUE details into class.
Honestly I would be quicker to recommend any of the above instructors than most cave instructors I see every week in Florida. We have some instructors here that are on the same par as the above (like Ken Sallot), but I also think Fl is more of a crapshoot in the quality of instructors compared to those I named in MX.
