Alona Beach being the premier spot on Bohol, its my preferred place to stay because of the (small) variety in nightlife - few bars, different restaurants (although somehow i mostly end up at the restaurant of Alona Tropical on the beach, also like the AT best to stay). The beach at the east end (in front of the Alona Tropical) is the widest, palm fringed and quite beautiful. Also marginally less cramped w/ the dive bankas. The first say 100 - 200 meters of the sea are shallow and covered w/ grass and those starry buggers with big spines that really hurt if they sting, forgot the name. Beyond is the drop off which is great for diving. Guess its about 5 to 8 meters deep when the tide is high so may be a bit too much for snorkelling. Also quite an end away from the beach, i am a comfortable swimmer but still, long way. You could ofcourse snorkle the shallow part. Think its pretty similar on the western part of Alona Beach.
Dumuluan Beach is less crowded, less wide and there was only one big hotel in 2005 when I was there. Owned by the local major, it caters to the japanese market (i know cause we made the flyers the major distributed at at Tokyo convention).
Panglao is a great place for divers, but I would be hesitant to bring a non diving girlfriend for the total lack of non diving entertainment (other then sipping gin tonics at the beach). But then, my girl usually beats me to the water, lucky me.