Well you won't hear much different around here. I have owned, built and run more car engines than aircraft but my first choice is still a strong 4 cylinder aircraft on a light boat.
I guess to be truely accurate is to say the best eninge is the one on YOUR airboat.
Different engines do different things. Automotive engines are heavy, then add a redrive and your way out there weight wise. If you just DD it then your still heavy just with with less performance. Aircraft engines are load sensitive since they generally don't develope the same HP as the hot rod Auto engines. However they are lighter, simpler, smaller and an old proven technology just like the aging original Chevy Small block V8s
On the Mini end is a whole range of boats and motors that really are super light weight.
Your performance from any of them is going to be related to all-up HP per POUND and hull shape.
My choice for my next boat is an O-360 on a light Palm Beach hull but I may end up with some BB monster and a redrive on a big hull. You can learn to run anything.
Safety should be a primary concern just as important as WHAT type of boat/engine you get. Learn from the really experienced, pay attention, practice, don't get in a hurry. You won't learn it all at once or even in a year, or hahahah even in a lifetime.
It comes slow in little steps. Sometimes 3 steps forward and 2 backward. It's one of the most fun things you can do. Always remember to put your family ahead of your boat though. It can be an expensive sport.
Welcome to the SA forum, glad to see new folks speak up. You will find all the help you can imagine on any airboat topic you can imagine here. Were all willing to share and show and discuss.
Let me show my lack of shame at this time by pointing to the site support link in blue just under your name when you post. The place is probably the best resource on the internet and it doesn't run for free. Contribute anything you can, and if you are unable thats fine as well your always welcome here.
Scotty