I was in Bali for a couple weeks this past September. (Big thanks to those on this forum for recommending). I cannot say its the best, because its the only place I've stayed, but OK Divers in Padangbai was excellent. Here is my plug- The resort is clean, new, pretty, affordable. The food is incredible (breakfast included with the room, lunch included with the price of diving). The spa services are somewhat lacking, but thats not my cup of tea anyway.
The OK Divers dive shop was excellently run. We spent about a week there. We asked to go to Gili Biaha, Tepekong, Mimpang, Crystal Bay, Manta Point and Nusa Penida. They arranged all of those for us and took us to several other sites we greatly enjoyed. They have a very nice (and fast) boat "Dipe boat too." We asked to see Molas, mantas, white tips, and pygmy sea horses. We saw all of them. Although, the Mola was from a distance and some prick swam directly at him when he appeared, so he retreated quickly. The mentioned dives sites can be dangerous (or so I'm told), we felt very safe with OK divers. The one thing I'll say, Crystal bay was extremely crowded and OK Divers didn't get us there early (like others have mentioned). I have a feeling this is key to seeing the Molas there.
From reading this forum, it seems like there are several shops in PB/Candidasa that offer excellent diving services. We enjoyed OK Divers and plan to go back someday, when we've checked more places off the bucket list.
In terms of wetsuit. I struggled with this big time when researching for the trip, so I'll gladly share my experience. I grew up freshwater diving in 40F water in Illinois. My wife on the other hand wont get in swimming pool in Dallas until mid June. I took a 3mm (brand new, so it was a warm 3mm) with a 1mm hooded vest and an underarmour thermal. My wife took a 5mm (she tried on a 7mm and couldnt move in it) with a 5+3 hooded vest. We were both cold at manta point (64F was the low on my computer I believe). Crystal bay got down to 70F or so. I am told we were lucky for water temps, and that it can get much colder. Even some of the padangbai reefs can have current that blows 70-74F water at you, which is chilly when not expected. Bottom line, be prepared for some cold water. A 5mm with a hooded vest is probably ideal. Even on the warmer dives in PB, you wont regret having the extra thickness. Then when you go up to Tulamben for a few days (Which I highly recommend), you can dive in a swimsuit.
