We trained for our Open Water with El Mar a few years ago and then went one one of their Mexico bus trips more recently. The classroom and pool training was simply outstanding. The course staff was very knowledgeable and professional and the facilities are just right. Similarly, I was able to get my Advanced Open Water on the Mexico trip. Although I had not planned on doing so, the staff talked me into it, for which I am actually quite grateful.
Their store is very well stocked and prices are good, with knowledgeable retail staff as well.
We did our actual Open Water dives in Hawaii, but the folks at El Mar were very helpful and gave us everything we needed. When we got to Maui and did our dives, the Course Director with whom we dove remarked that our training had been superior, compared to most of the tourists with whom he completed Open Water dives.