Hello there! Good choice sticking with Pentax if I may say so. Now which model is best for you depends on your budget. If you have a budget of $900+ and already have lenses, then without hesitating I would recommend the new K10d. Weather sealing(!), effective shake-reduction system, bright pentaprism viewfinder, 3fps continuous shooting which will go uninterrupted for 9 frames with RAW or until the card is full with Jpeg, shoots in Pentax RAW or Adobe RAW format, 10 megapixels... it's about as close to perfect as I think you'll get near this price range.
If your budget doesn't stretch that far, I also have no hesitation recommending the K100d. For an entry-level dSLR it's solid, well-balanced, extremely well featured, and performs very well indeed. The K100d has a small buffer so it's not the camera to go for if you want to take hundreds of continuous shots of moving subjects, but I don't so it's not a problem for me. It's lowest ISO is 200, although in practice I've never found this to be limiting, and it goes up to ISO 3200, which the K10d doesn't. Add in the anti-shake feature that's also in the K100d and you have a camera that is particularly ideal for low-light handheld shots.
As for manual vs program features, the K100d has several program modes which I never use. Ever. But this doesn't bother me, as I simply set it to aperture priority and use meter lock and/or exposure compensation, or I set it to fully manual. The only thing I would say is, make sure you use lenses with the A setting on the aperture ring. Those without will work, but it's not so easy to meter with them.