Oh boy, that's a tough one.
You need to set out your own criteria. What is important to you?
For example, take a look at the picture found here: http://ambergriscaye.com/pages/lodge/longview.html
Go far over to your right and you will find the location of the Seven Seas. Notice how it is just a shade north of the main town and how it is not really close to another hotel (as in right next door). Unfortunately, this picture only goes as far south as Ramons and Mata Rocks is quite a bit further south of town than that.
Then also take a look at this map of San Pedro and many of the resorts, etc. found here: http://ambergriscaye.com/pages/town/mapdowntowndetail.html
That might help you have some idea of their locations relative to the main part of town, as in, proximity to Fidos, Jambels, Big Daddy's, Estel's, BC's, Sharks Bar, Ambergris Delight, Cholos and so on.
You may also note that Mata Rocks is right near Banana's.
The Seven Seas is an interesting little property. The room that I saw was not as large as the one I see pictured on their website but it was adequate. My concern was that due to the layout, there might not be enough air circulation in the suite, especially in the bedroom. I really liked the location. However, if you book there, make sure that they guarantee you a room with an ocean view. They are building some more units in the back. I'd be really ticked off myself, if I booked with them and that's where I ended up hanging my hat.
Also, the Seven Seas pool, while a decent size (qualify that with "by SP standards") is in the back of the property behind the resort. I can't imagine that it ever gets much sun. Perhaps in the morning and a small part of the mid afternoon, if that.
I very much liked the front yard area, it's pretty with lots of palms and such. The beach area immediately out front, is not all that.
Sorry, I can't speak more to Mata Rocks. Hopefully, someone else can fill you in.
Good luck with your decision.