I think the key factors are the distance you are fishing at and where in the surf zone you are trying to play the fly.

If you are fishing the water close to you and are working the fly primarily in the waves at your feet or immediately in front of you, then a floating line works very well. If you are casting beyond the first wave, then a floating line rides up the waves and creates slack between you and the fly, preventing you from feeling the fly. In those conditions, I prefer an intermediate line. Most of the areas I fish are too shallow for a fast sinking line-- I'd be in the bottom all the time-- but I can see the need on more sharply sloped beaches.

Outside the surf, I frequently use a floating line if I'm fishing flats or river outlets, particularly if there aren't any waves or chop. If there are waves or chop, then I find myself preferring an intermediate.

MM