Never heard of Hotel Waterfront? Is lovable Eddy turning sarcastic on us????
I have stayed at Sosua by the Sea a bunch of times, it is nice, but not near the "town beach", it has its own little beach behind the hotel which is nice. The town beach is a little bit of a walk away, probably 10 min. But it has nice rooms and all of the amenities you mentioned, I don't know how informal they are on their guest policy though. I did have a nightmare issue with paying with a credit card there once, you should know. Long story - bottom line is they charged me twice and claimed they didn't. But all in all I have had good experiences there.
I've never stayed at the Waterfront but I've heard good things and eaten there once. Very nice dining room, and the staff was very friendly too. A bit closer to the town beach.