Those of you who have done extensive traveling...which of the islands do you prefer?

Is this a question designed to help you find which you'd like best?
If so, you'll need to post the specifics you're looking for to get a good answer tailored to your tastes.

The reason I mention this is that some people love GC, some love SJ, some love both, neither island really turns off very many people. You'll ind lots of favorable comments about each.
But these islands are night and day different...not at all comparable.
GC is flat and has little vegetation, commercialized, safe, great snorkeling, good food, lots of tourism and hotels/condos.
SJ is lush and tropical looking, has great beaches, much more isolated feeling, less touristy, very few hotels, limited food/shopping comapred with GC.

Oh, and in answer to your actual question, I suppose I slightly prefer GC. The reason is that GC is a great beach only destination (that is, if I'm not looking for solitude, scenery, withdrawing from society type trip).
SJ is for the opposite purpose IMO.
But if I want scenery and solitude on an island there are other islands I prefer over SJ.
To me each island serves a different vacation purpose. GC works better for its purpose than does SJ for my tastes.

I agree that it depends on what you want. I think that St. John is more of a must-see for those who enjoy nature. We enjoyed spectacular views while we were there. Obviously we prefer St. John.

St. John to us had it all. Just beautiful. The scenery, views and those "beaches" absolutely breathtaking.

The town of Cruz Bay is so picturesque with great shops and restaurants. Can't think of many islands that can compare to St. John with those picture perfect beaches and views to die for. It's an island that you want to drive around to explore the many beaches. It's so small, it only takes 30+ min to drive the whole island. The only other island that comes close to being as picturesque is Bermuda. I always compared every island to Bermuda until we went to St. John.

We were so glad that we rented a villa instead of going to a resort. You get a lot more for your money and you can't beat the privacy, plus so romantic.