Both are beautiful, and it depends on what you are looking for:
-Sapphire Beach is part of a resort. You are allowed to use the beach without a problem. There is a marina, so if you wish to parasail or jetski, you can rent there. There are no changing facilities to speak of, other than the rest rooms.
-Magen's Bay is less commercial and more wooded. There are more areas to just relax. Even so, there are refreshment stands and changing stations.
I'm sure you will enjoy either.
consder coki beach too, I haven't been to either of the ones you mentioned, we chose coki after much research. for us, we loved the privacy yet it had all the amenities other than motorized sports. 5 mnutes past saphire.
we've pictures of coki here at destiny, southern caribbean 04 in the photo gallery.
i'm trying to decide on a beach too for St thom. I don't just want to do the same one.... but loved coki.... who knows... more research!
Magens Bay is one of the Top Ten beaches in the world. We spent a week in a villa along the north shore of Magens bay and spent a number of wonderful days at the beach. It is quiet and beautiful - while there is a bar and some facilities for bathing/changing/picnicking - it's not as commercial as some other beaches on Saint Thomas. Bring snorkleing gear as there are some nice coral gardens along the edges of the bay....
IMO is WELL worth the trip to the Island of St. Johns if U are looking for a the premier beaches in the USVI. There is NOT a Bad one on that island and it well worth the 1 hour taxi and ferry ride time to experience either Trunk Bay, Cinnamon Bay or Honeymoon Beach. :thumb
I can't comment on Magens Bay Beach being that we have not been there. However, we have been to Sapphire Beach this past October. It's very nice, the water is of course beautiful, snorkeling good, the beach has one side with trees for shade. You can rent lounge chairs for $5.00. We enjoyed ourselves there.
As E just mentioned, if you have never been to St. John, Trunk Bay is a must do. it's really beautiful there.
I've been to Coki, Sapphire and Magens Bay. All three beaches are very beautiful. I prefer Magens bay because of it's setting, white sand and beautiful cactusses, palmtrees and green hills along the beach. Definitely prettier than Sapphire beach and much longer than Coki beach. Coki beach is a very nice small beach with white powder sand. After 2 hours I was boring and we took the cab to Magens bay. I made soms great pics of Megans and Coki.