I am not sure if you have gone to a camera store and had a play. That is truly the only way you will know what YOU like.
Personally, I have used Nikon D200 and the Pentax DL and K10. Only once ever looking through a viewfinder did I ever go WOW that is big and bright and that was with a Canon , but that was a pro level EOS-1D. Most a very similar.
It is not until you have one in your hands and then swap directly to the other model will you see for yourself the differences, if any, and whether or not they are deal breakers for YOU.
The Pentax K100 takes great pictures and the SR is a deal maker for some. The Nikons have always been known for fast AF, Pentax are known for ACCURATE AF.
Pentax also offers a huge range of lenses (old and 3rd party) that can change how you do your photography.
My suggestion to you is to get to a camera store with both models and have a hands on feel and play. Thats how I came to my decision to buy Pentax, how it felt in my hands. If you are not comfortable then look at something else.
There is no such thing as the perfect camera for everyone.
I hope you find a camera that works for you and allows you to take the pictures you want.
Lastly, image quality and results are very similar between all camera makes. I have yet to hear of a situation where someone has gone, "yuck" or "My god, what camera was used to take that picture, it is terrible."
I have been amazed by comments by different people about image quality of different brands/models and so forth.
I believe that if someone posted a picture on the forum, no-one without looking at EXIF data, could say whether the picture was taken with Pentax, Nikon, Canon, Olympus or so forth.
Good luck with your camera choice and I hope you like the PENTAX, because we do..