To get the most bang for your buck, i'd shop used. I've already gone into the old iron approach, but if i were shopping for something 5-10 years old, i'd look at Delta, Makita, General / General International, Shop Fox, Jet, Grizzly, Woodtek, Bridgewood, Dewalt, and maybe Ridgid. Rikon and Steel City also make good machines, but are fairly new to the market. Hitachi also makes a highly regarded combination planer / jointer that i'd certainly look at. They may have a portable model out as well, i don't know.
I'd also look at the Craftsman and some Ryobi, but would expect to pay less.
They'll all plane wood well. One of my cousins has a 10" Ryobi that he purchased several years ago for the barn shop on his farm. It's not an expensive machine, but has handled A LOT of lumber over the years in less than ideal conditions with no problems. It's no cadillac, but the thing simply works and works well. If it died tomorrow, he'd replace it with the same thing if he could. There's not much reason to get brand snooty.
Just about any decent woodworker can get used to any decently made machine. It's also pretty easy to get bad results even with the best machine. I agree that no one should waste money on junk, but bells, whistles, and brands name don't make good woodworkers.
The Craftsman you're looking at is not one of the Parks machines. It's much newer. It looks like a 12" or 13" portable unit. If so, $400 seems a bit steep. For the same money, you can have a new machine with the same capacity.
If shopping used, it should be pretty easy to tell if a machine's been well maintained or abused.
Another thing to consider is the blade type. Disposables are convenient, but can get expensive over time. If you've got the sharpenable kind, that's a maintenance item. I've had blades sharpened, and it wasn't very expensive, but you'll want an extra set of them so you can have one in the machine while the other is out for sharpening. Or, you can purchase a setup to sharpen them yourself. A good portable machine that uses sharpenable blades is the Dewalt 733. It's essentially the same as the 734, which uses disposable blades.
Paul Hubbman