The right pump is a big debate, there are three main points for each:
Size of the boat.
How heavy of a load you intend to carry.
What type of water you intend to run in.
The single stage pumps, like American Turbine for example, are great for high speed running in deeper water, with a smaller boat (20-22ft) and a lighter load, like a couple people, gear, a dog, etc. American Turbines have aluminum impellers which are fine until you suck up a rock... . bad day in a big way. Single stage pumps also cavitate like a ***** in shallow water, or in fast-moving river water. Single stages are also pretty much worthless for any slow speed manuvering.
Three-stage pumps work better in shallow or fast moving water, usually have stronger construction (ability to handle more power), take more of a weight load better, and most have stainless steel impellers with stronger thrust bearings. The most popular of these are Kodiak and Hamilton, but XStream is out there, too. Hamilton makes some BIG pumps, too. Anything over a 212 is overkill unless you need to haul 6+ people all day every day. My preference is to Kodiak, as the Hamilton is more $$$ for essentially the same thing, and the XStream I don't know much about, although I've heard they are easier to work on that a Kodiak or a Hamilton.
For a boat, my preference is to Duckworth. Own one, love it, hope to buy a bigger one in a few years. The biggest reasons I like them:
-Build quality--they're put together better than anything else I've looked at, and I've looked at pretty much all of them.
-Handling--they don't slide in corners, they don't porpoise up, and the ***-end doesn't sink too far into the water under part throttle like others do.
-Customer Service--you're buying into a family and they treat you like it.
Another combo to look at are the 20-22's with the Mercury Sportjet setup--Motion Marine makes a great line of boats with the Sportjet units, too.
Be on the lookout for a used Duckworth Silverwing, with a 350 Vortech or 351 Redline and a Kodiak pump. Thank me later.
Hope this helps,
Dan-