It's very difficult to recommend one camera over another. All the dSLRs from all the makers are good and frankly at any given price point there's not a lot between them. It comes down to budget, how a camera feels in your hand and any particular feature one model may offer over the others which is important to you.

The Pentax K20D and the Sony a700 are mid range/semi-pro type cameras whereas the Sony a350 is "entry level" - but it does have a lot of pixels and the best "live-view" yet offered from any maker. I have one and am very happy with it, but I do have an a700 also

In many ways the lenses are more important than the body so whatever you get try to budget for at least one good lens - unfortunately this is likely to cost as much as the body