There's diving in the Phils throughout the year, but stay away during Monsoon Season June - early November. The trips are extra cheap, but they are also very unpredictable b/c the typhoons really do hit the islands hard. It's better to leave the last minute cheapie deals to the locals and stay safe
If you're planning on going mid-March - April, Tubbataha reef (smack in the middle of the Sulu Sea) is supposedly really awesome as it is only diveable for a month because of rough conditions the rest of the year. Puerto Galera & Puerto Princesa are the main dive meccas and it's mostly wall diving. Nothing really in Cebu or Manila but there are a lot of tours that book out of there.
Diving in Asia is generally split into either reef diving or just hanging in the blue waiting for Mantas, Whale sharks and the like to show up...(but sometimes they dont)
