Well, since we just got back from seeing several of the ports that Mariner is going to, let me add my two cents.

Costa Maya is interesting; they have created a complete all-inclusive cruise port complete with swimming pool. There are shops and restaurants set up all around the pool, including the ever-present Diamonds International and Tanzanite International. There are plenty of arts and crafts, too. But they are far more expensive than say, Cozumel, and they aren't happy about being open when there is only one ship in port. We didn't sail until 5:00, but they all closed up about 1:00.

Belize has pretty much the same set-up, but more spread out along the waterfront and it isn't as new. I didn't talk to many people in the shops, because it was hot and I was tired; we rode the tender in just to say we had been there.

Santo Tomas, we didn't get off the ship. They have a big warehouse-looking thing that they set up booths of arts and crafts in. As we got ready to sail away, there was a parade of about 32 taxi's with flashing red lights on their roofs. They parked in a line, and honked and waved as we sailed.

Roatan Island is where they put us on buses and took us to a marine park for a beach picnic. The marine park is immaculately clean, the ship's chefs provided us with an incredible lunch, and the water is beautiful. That being said, the island looks a lot like St. Thomas or St. Maarten "back when". Not a place that a lot of people would feel comfortable in just wandering around.

So, from my experience, the SS itinerary is far more attractive.