Interesting - I didn't know that American allowed dogs > 90 lbs (this includes the crate). I have heard from many that Continental is much more sensitive and animal friendly. Delta doesn't transport animals that size to Belize (smaller pets can be carried on or checked as baggage), so I think those are the 3 airline options for animal transport.

My experience? About 18 months ago, AA lost my 70 lb dog as they put him on the wrong plane and truly had no idea where he was for > 12 hours (it was pretty bad - I will spare you the nasty details), but bottom line is that I don't believe I will be using them again.