My DH and I want to take the kids and grandkids to the caribbean (or Belize or Costa Rica) next spring. The kids will be 14,16,18. None of us have been to that part of the world and I want to narrow things down because we want to rent a house and they will book early.

This is our list in order of importance:
On or very close to a WARM sand beach (it is snowing here today!!)
A town within an hour drive
We'll be flying out of Salt Lake City so it's more affordable not to go too far south in the caribbean.

Any and all help is appreciated

Manuel Antonio Costa Rica is very popular with families - a national park, lots of wildlife like monkeys, beautiful beach inside the park, and loads of restaurant choices - most everyone speaks English there, and it's very easy to get around.

www.manuelantoniopark.com

Hmmm...I'd pick Honduras. Roatán is gorgeous, has lots of rentals, and there are lots of options from one base (hiking, snorkeling from shore, excellent diving, good restaurants. If you wanted to extend your trip to another spot you could visit Maya ruins or hike and raft in beautiful jungle. It would likely be much cheaper than either Belize (which I love) or Costa Rica (which doesn't interest due to relative lack of snorkeling/diving and cultural diversity) and the airfares have been remarkably low lately (though don't know if they'll still be low when you're ready to buy). My photos are linked below if you're interested - happy trails!
http://www.flickr.com/photos/staceyholeman/collections (Roatán is in one of the 2006 collections).

My kids are thoses age and we go to Central America/Mexico often. Your first decision is whether you want a snorkeling/diving (Caribbean) or surfing (Pacific) beach. Which do your kids prefer?

Hope... I'll look into Honduras.

Cross.. Good question. The kids waterski, board and a bunch of sports, but have never tried diving/snorkeling or surfing. Always a first time, I'll see what they say.

Are you deadset on renting a place and staying put? Belize can provide an incredibly diverse vacation experience including hiking, caving, rappelling, incredible ruins as well as gorgeous snorkeling and diving, though it works best to split your stay between an inland spot and an island or beachy place. The Belize collection (same link as above) has photos from a really adventurous trip when our kids were 17, 18, and 20. This summer we're heading back and will be spending part of the trip with nephews who will be 12, 15, and 18.

We're open to most things I guess. BUT we only have a week and we want this to be a little relaxing

Good point - hard to be both relaxing and adventurous with just a week. We like to be adventurous first and relax a bit at the end and the cultural piece is a priority for us. We're blessed, though, since we usually have a month or so; my husband and I are both educators with summers off (and we spend less money in our month than most folks do in a week).

I stick by my Honduras option in that case.

you might consider flying to cancun. then travel an hour or 2 south on the coast. tulum is about as far south as is reasonable to get a good villa. i'd look within a 1/2 hour north or south of playa del carman - a good sized town with lots of shopping and restaurants, etc. the area has tons to do: zipline, golf/tennis, snorkeling, atv jungle tours, horseback riding, fishing, and ruins (tulum, coba and chichen itza are day trips) and great beaches.
we stayed quite far south on tankah bay beach. good snorkeling and Very quiet. not much for teenagers to do anywhere close.
if you're interested take a look at locogringo.com they list all there is to do and have tons of villas to consider. another good villa site is bill-in-tulsa.com and laura has a fun site: www.mapchick.com
locogringo's rental agents were most helpful to me. i described the villa we wanted - they sent back a list of 1/2 dozen, avail for our dates, for us to consider.
be sure to click on the tiny airplanes at the bottom of any given villa page.

Okay, I sent an email to each of the grandkids and their parents to see what activities will interest them. If each responds then I can start narrowing this a little.

Virginia, Playa has been also been at the back of my mind. We may be trying for a place no one has been.

Hopeful, My DH and I are not limited as we usually spend a month at a time in Italy.... BUT the kids are on school break so they have time problem.

perhaps after the family goes home you and dh could stay on in a condo. you'd have time to explore the sian kaan biosphere and drive down to belize if you wished.

i forgot to mention xel-ha and xcaret in my previous post. they are eco marine parks and loads of fun. xel-ha is smaller and more low key. xcaret even has a dinner/mayan history show.
http://www.xcaret.com/
http://www.xelha.com/