Isla Blanca for sure. I've fished quite a bit with Yucatan Fly Fishing Adventures as I used to book a ton of clients to their various destinations.
Their boat launch is about a 20 minute drive from downtown, they'll pick you up at the hotel and drop you off in the evening. Shots at Perm, Bones, Tarpon, and Snook. Time of year and tides determine what's around and how good it can be. Fishing at Holbox has dropped off a bit so a few of their boats will run all the way down, but not much pressure overall.
Marco Ruz is the proprietor and I consider a good friend, he has some really great guides that work for him, and he treats them well. Thee are a few independant guides down there that can be pretty hit or miss. If you make it please say hi to Marco and crew for me.
http://www.yucatanflyfishing.com/isla-blanca/
Dylan Rose at FlyWater Travel is handling their stateside booking now and is down there yearly so he can give you a ton of details.
http://flywatertravel.com/destination/CancunMexico
If you had more free time and were going in the summer I'd highly recommend Tarpon Cay Lodge near Rio Lagartos. Probably the most fun destination I've fished in the salt. Owned by the same folks.
Let me know if I can answer any more questions.
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