Cabo San Lucas or Belize is where I'd go.
On my honeymoon back in September of 1986 we went to St. Thomas. Did a 1/2 trip where I caught a #216 blue marlin. Was back in St. Thomas in August 2005 and the place had changed for the worse. Did get out fishing, real slow day as all my son and I got was a lone #12 blackfin tuna.
One thing you might want to consider is doing a little research on what specie(s) are available in the locals you are considering for that time of year. As some places might not have that great a fishery during the time of your honeymoon.
