1. Mactan Island in which the airport is located.
a. Daily commuting between Cebu City and the dive operator will be too tedious as the traffic can be horrendous. And if you do decide to move to Mactan then make sure you select a suitable place because in certain area eg. Maribago and Marigondon, Korean is dominated.
b. Which operator? This is the most tricky part!!! Speaking from my limited experience diving from Mactan, single diver is NOT being treated favourably. Some of the sites are very good but whether the operator will take you there is another matter.
2. Moalboal which is about 2hrs away by good road. Public bus is plentiful and safe.
Everyone is talking about the 'sardine" and you won't be disappointed. Dive with Nelson and stay at Eve's Kiosk. There are up-market places as well.