Cannot comment on the Sheraton specifically but did stay at the Banyan Tree at the Laguna. HATED the whole area. Most of the hotels seemed really dated. Shopping centre was horrific and were constantly pestered to look at properties. Had to cross the road to get to a pretty awful beach (may have improved now as this was about 18 months post tsunsami). Sheraton may be OK, but the resort is very Butlins-esque.
We wouldn't normally stay at a Marriott (hate large resorts ) but went the the Phuket Beach Club to meet friends for a long weekend and the children just loved it and we were pleasantly surprised by how much we enjoyed it. Defintely a long way from Phuket town etc, but if you just want a family beach/pool holiday, it fits the bill.
Laguna is nothing like Butlins (with the exception of Laguna Beach maybe).
Dusit and Sheraton are on the beach, no roads to cross. Allamanda you get a boat.
Banyan Tree is up itself, overpriced and full of knobs. It is however undermaintained, I can well understand why someone would be fed up shelling that money and then getting there.
If you really want a villa there are new ones on the golf course, this is far from the beach though (but still just a boat ride).
Marriott tries to sell you timeshare as well, half the resort is one, it is no better or worse in this respect, you get invited to a presentation, you say no and they leave you alone.
As for beaches, PP clearly went at the wrong time, Bang Tao is way way better than Mai Khao(?) which is I think where the Marriott is. Even if I got the beach name wrong the one at Laguna is better, have stayed at both several times.