Gator,
I agree with Sunil, why choose? Why not both? Chances are that you will have Gambusia regardless in our area...they are one of those fish that just appear in our area. However, stocking a few initially will get things rolling in the right direction.
Fatheads provide great initial forage for your predators but generally do not survive predation more than one year. Gambusia, on the other hand, will survive through reproduction and their ability to use very shallow water to hide in indefinitely. Gambusia are small, but many small bites add up.
If its one thing I've learned from the GG experiment, Gambusia are one terrific forage fish for hybrid bluegill. Before starting that experiment, I knew small LMB and larger BG fed heavily on Gambusia in my ponds based on observations and stomach sampling...but no kidding, the GG's absolutely slaughter Gambusia...even in 52 deg water temps, I have observed GG surface blasting of Gambusia. I'm more convinced than ever as to the value of these small fish to your low end predators....small LMB and BG, and especially hybrid BG.
