We stayed at Sirenis last year and dove with Blue Caribe, which is headqurtered at Be Live, but will gladly pick up from Sirenis on the way to their launch site on Akumal Beach. They're very reliable and prompt. Here's a trip report I wrote last year:
My wife Sarah and I visited the Riviera Maya south of Cancun from July 13-22, staying at the newly re-named Be Live Riviera Maya (formerly Grand Oasis Riviera Maya) from July 13-18, and the Grand Sirenis Riviera Maya July 18-22. I’m filing separate TRs for the GORM/ Be Live (which I’ll refer to here as GORM) and the Grand Sirenis.
The on-site dive operation at the GORM was Blue Caribe, and you couldn’t ask for a more customer-friendly (for that matter, just overall friendly) dive shop. First, they communicated quickly and consistently by email, so I was able to easily make advance arrangements for us to dive the day after we arrived, even though the shop was closed by the time we got to the hotel on July 13. Second, their pricing policy is very fair. They may not be the absolute cheapest in the Akumal area, but they have a sliding scale, so the more you dive, the less you pay per dive. And you don’t have to commit in advance to buy a specific number of dives in order to get the package price, as we have encountered with other dive operations. You just dive as much as you want during your trip, then at the end, you pay according to their formula for the dives you did. (For 6 dives, for example, the cost is $210, including weights and tank, but no other equipment.) And the divemasters Emiliano, Laura, and Alex are the best! Very professional, and once they’re sure you know what you’re doing, they don’t hover. We had our own computers, and they let us basically stay down until someone ran low on air or the computer said it was time to surface. They have an obvious passion for both diving and customer service. We saw some really nice reefs, with lots of small tropicals and a good assortment of big stuff as well, including big groupers, tarpon, turtles, and barracuda. All of the dives leave from Akumal Bay, so Blue Caribe picks up and drops off clients from the hotels in the vicinity. They were very accommodating about our schedule, and provided round trip transportation whether we were doing 1 or 2 dives each day. They also dive in the cenotes, which is unique to this part of the world. We did a cenote dive on a previous trip, and although it is definitely something I would strongly advise you to try if you’ve never done it (unless you’re really claustrophobic), we thought that once is probably enough.
This is I think the only place in the world where you can reliably swim (between June and September) with whale sharks, which are the world’s largest fish, but totally non-threatening (unless you’re plankton 
. We really got excited about this, and signed up to go. Unfortunately, we had terrible luck. The weather was not so bad as to cancel the trip early, but it took a turn for the worse after the boats left the dock, and an hour out on the water, we had to turn back. (We were informed that this was the first time within anyone’s memory that the boats had to turn back after departing.) So we basically wasted half a day (starting at 5:45 am!). However, Blue Caribe has a guarantee policy that you’ll get to swim with the sharks, so we had the option of getting our money back or re-scheduling. We tried to re-schedule, but once again had really bad luck with the weather. At least this time, they cancelled the trip early in the morning before we the hotel, so we didn’t waste the day. We were bummed, but at least it didn’t cost us any money, and we can look forward to doing this in the future.
