I have used both. They are both good. Tropic flights seem to have more punctual departure times, but Maya will give you a 20% walk-up discount when you pay cash. We usually go with Maya because of this discount. That saves you about $24 US per person on each round-trip ticket to San Pedro. That adds up, especially with that many people. I would email them and give them a heads up that you will be walking up with that many people so they can plan accordingly.