I bought the K10, then the K20, but not the K7 because the sensor had no improvement over the K20.
However, the K5 sensor files are head and shoulders better than any previous aps sensor. They are so much eaiser to pp than the previous digital files i have worked with. Sony has the hot hand, thats for sure. It isn't just the K5, that same 16mpx sensor with 25,600iso capability (extended to 80iso and 51,200iso in the k5) is terrific in the Nikon D7000 and even the Sony Nex5n. I've taken dress rehearsal shots for the local playhouse at 20,000iso that turned out lovely. (12"x18" - wouldn't go larger than that
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If i was going to buy a camera other than Pentax, i'd make sure it was a Nikon or Sony, just because of the excellent sensors in them, not sure why Canon seems to be lagging in this area. The Fuji X Pro1 also seems to have an excellent sensor.
Obviously, you want top video capability, I'd wait till we see more from the K30 test images, should start showing up after June 25th, if i remember. Looking at the spec sheet, they boosted most things that were in the K01, which was already an improvement over the K5 in video. Canon has always seemed to lead the way on the video so that might be the reason to go there.
Why Pentax? i'm put off by the large camera bodies and now lens bodies that are the normal in Canikon. The optical vibration reduction systems that have been incorparated in Nikon, Canon, many Tamron and Sigma lenses just look bloated (heavier and larger volume) over Pentax and m4/3 and Fuji lenses. I would guess it has something to do with the VR/os mechanical stuff. The WR is another factor. The Pentax menus, i find easy to remember and find stuff. Also love the quiet shutter in the K5, just hate noisy shutters for theatre work. so i guess its a bunch of things.
Anyway, you can take good pictures with any of the digital cameras today, they all have some features better than others, and some worse. Find the one that fits your style of shooting is my advice.