It comes down to what you're trying to get out of your brief 4 day stay. If you want fine dining or shopping every night with a touch of beach or swimming pool, then do Ft Lauderdale. If you're going for whimsy with a little head scratching about where to eat each night, the Singer Island resort is good for BF every day and one nice dinner. The other three meals can be accomplished driving locally no more than 15 minutes -- the dining choices in both Lauderdale and Singer Island are immense ( in all price ranges ) and concierge can make some great suggestions at either end. So I'd focus upon whether you want a more urban feel ( which the Lauderdale resort is more proximate to ) or an in-between where you're on a relatively laid back island but in very close proximity to night life and food. Although the Singer Island hotel sits admist hi-rises, a 3/4 mile walk south towards the inlet takes you to the village of Palm Beach Shores which is low rise residential with quite streets and walking paths. The Sailfish Marina is located here ( great place to stop on Thursday nights when they have vendors hawking their wares along the water, but middling food in my opinion ).

Lauderdale would allow you to forego a car rental. Same possibility at Singer Island where a cab to the resort should run $35. We go down 3 to 4 times a year and we rent a car when the rental rates are right and otherwise we use a taxi -- we guestimate how many times we'd use a taxi and we cab it if our aggregate cost will be less than the rental price. It really come down to how you want to spend your days and how many nights you want to dine out and need a cab versus eating local. The water taxi at the Sailfish Marina doesn't run every night, but that too could make for a "walk and float" sort of night out in West Palm on Clematis Street.

The beach here is smooth sand and lots of it and there are spots here and there where one finds lots of shells depending upon the tides etc. The snorkeling in the immediate area is very good. Concierge can arrange this as could the beach concession just up the beach at the Marriott timeshare resort. Parasailing & kayaking are also possible ( kayaking either off the beach, or guided tours on the inlet side ). Not sure about the Lauderdale area, but the surf on Singer Island has lots of manatees, rays, dolphins, and sea turtles. June is a time when the turtles should be bobbing about, especially at dusk and dawn.

Marriot choices sure are fun.

Barry