I'd likely stay as small as possible . . . not much to gain stepping up from 2.5 to 5.0 HP, I'd think, for 10' Pond Prowler.
I think the Suzuki 2.5HP is one that is always reviewed very well. Not a bad new price either.
The one I think I'd avoid, and the one I'd buy over all others if they ever get a few quality control issues under control?
A Lehr 2.5 HP that runs on Propane . . . everything from those small green propane cans . . . to large propane tanks. That'd be so handy, so easy. They get great mileage, much less emissions. Alas, they are finicky and have some issues.
That others aren't available, especially in these small outboards, is a travesty. They'd sell like hotcakes I think.