Are you into scuba diving and fishing?
If so, then Belize is your Mecca, but it WILL cost you, unless you're going with a group. Mexico has better ruins and better prices on just about everything (even in some of the tourist traps like Mazatlan, Cancun, Puerto Vallarta, etc.) However, Belize is tops in Central America for diving and the fishing is oustanding (I only know of one place better for fishing, and I'll burn in Hell before I give that location up). You pay for it, though.
If you're into the beach scene and taking it easy, go to Mexico and save yourself some money. Most places in Mexico (excluding some spots in the interior) are like taking a trip to South Beach in Miami, so I wouldn't worry about the language barrier.
Or, do what I do. Go to Costa Rica. I've been to a number of countries across 5 continents and I've yet to find a better place to visit. All I'm saying is that your money may be better spent in other places apart from Belize, depending on what you are looking for.
Heck, I've seen $300-400 airfares to Europe recently, so keep your options open...
If you're looking for some quiet, stunning spots to seriously get away from it all, I know of 5-6 in Mexico and about 2 dozen in Costa Rica. PM me if you're interested.
