I suppose that it comes down to what you want to use your receiver for. I listen to music 95% of the time, movies 5% and I recently auditioned all three of these receivers.
Flat out, I didn't like the sound of the Pioneer. It was the first of the three I listend to and after hearing it the first time I knew it wasn't the one for me. I can't give you any real specific reason why, I just didn't like it.
The guy at the audio store suggested the Yamaha if I wanted to use my receiver mainly for movies, but that wasn't a strong selling point for me (refer to afore-mentioned 5%). I found the stereo sound on the Yamaha to be inferior to the receiver I was replacing, so the Yamaha was out.
Luckily for me, I really, really liked the Denon. I had read a ton of very positive reviews about it (the best of which was on this site), and I found that for both movies and stereo it had a sound that just worked with me. In the spirit of full disclosure, I will admit that I am a little biased towards Denon in the first place.
To be honest, I'm not sure what you mean by "The power seems the truest on the Pioneer?", but the Denon puts out a lot of very clean power, and I have no complaints with it in this regard (if this is what you are talking about, if not just ignore this paragraph).
Good luck.