Check out Los Suenos resort. A friend of mine has his boat down there. A few of our friends have been down and they said the place, the fishing, everything is AMAZING!!! I am pretty sure the past couple of months (March-April) are the best time to go. They fished a big time tournament there at the end of March, so fishing wise, that is probably the best time.
http://www.lossuenosresort.com/