I like Ocean Boulevard, but having stayed there this past August, I would not suggest staying there for Easter week. I had the opportunitity to book a 3 bedroom at Ocean Boulevard for this Easter week but I opted for Hilton Head, instead. The reason is the weather. Things are not any better in Hilton Head, but the pools at Ocean Boulevard really stink. They are freezing, even in the summer. The pool in tower 4 is okay, but the ocean front pools are in almost complete shade all day long and the three towers create some kind of wind effect by the pool so in additon to there being no sun, it is windy. In the summer, this is okay but in early Spring, I think it will be too cold. Plus, Ocean Boulevard does not do a good job heating their pools.
I've never been to SeaWatch but the pool situation at that resort seems better. Maybe SeaWatch actually heats their pools to a comfortable temp, too.
Ocean Boulvard is nice, lots to walk to from the resort and you can even bike to a lot of things, but the ocean anywhere in the Carolinas will be like ice water and like the other posters mentioned, if it is cold (and probably 60% of the time it is cold and wet), being by the beach is not fun.
I've gone to Hilton Head more than a few times over Easter break and when the weather is good, it is great and it feels like summer. I would immagine Myrtle Beach is just as nice over Easter when the weather is good. Probelem is more times than not I have been to Hilton Head over Easter week when half the week, if not most of the week was mid 50's and rain. Talk about being miserable!
Lots to do in Myrtle Beach beside the beach. Many more things to do than Hilton Head but if you go, prepare yourself for cold weather and count yourself lucky if it is actually warm enough to enjoy the pools. Also, if you go don't take any nice days for granted -- get to the beach and pool, even if you had other plans for that day because chances are pretty good the next day will not be so nice.