Don't let the price of the super tiger engines fool you. Their engines are rated by BHP which is the power that it takes to stop the engine. I have ran a number of different engines, and so for IMO the EVO's and the ST have been the most reliable.
Ex: the ST G45 Power Output: 1.45 BHP at 16,000 RPM, this engine is super reliable, and will push the boat your showing like a bat out of hell.
The Evolution .46NT is guaranteed to start quickly and easily, this is another good engine and will hang in there with the best of them.
As I said before most all of the aero engines work well on airboats, the key things are have the correct prop for the boat, and have the carb set.
A good tip for any engine is take it down and clean up any casting marks, and check to make sure the the top of the cylinder is smooth and flat.