We have done both. While the scenery on the 5 Star was breathtakingly beautiful (see photo below), a gorgeous beach, we had a lot more fun on the Golden Eagle.
5 Star is a boat ride over to the beach area. A dinghy brings you to shore, or you can snorkle right off the boat (Leylon Sneed?). There were no floats or anything to play with in the water provided, but it looked like the snorkelers had a good time. It is one of the most beautiful places I have ever seen, so it was worth that alone.
The Golden Eagle is a funfilled adventure (about five people got seasick, so take your Bonine) with an extremely fun crew and great island music. When you get to the beach area, you must swim over to the beach, which isn't far, but the water is over your head. It is very easy to get off the boat, even with kids, as you have noodles for floating. They provided mini-submarine sandwiches and drinks on the ride back. We had a great time, one of the highlights of the trip.
On both excursions, some feel there is not enough time to enjoy the beach. I found it worked out for us, though, because the Golden Eagle early morning excursion left us plenty of time to shop.
You can't go wrong with either. I guess I prefer the Golden Eagle, if I could only do one.
Here are some previous threads on the subject:
http://www.disboards.com/showthread.php?s=&postid=5970160#post5970160
http://www.disboards.com/showthread.php?s=&threadid=612661
Have fun!
Tink