Here's my thinking: buy it from somewhere that will take it back (preferably without a restocking fee) and try it out. If you like it, then your search is over. We can give you advice on specs and such, but your own personal preference is what really matters.
Personally, I'd probably pick the Pioneer because I have been very happy with my 1015 (and I've owned Onkyo and Yamaha). Some people here swear by the 663, so I'm assuming that it's pretty good. My brother always buy Sony receivers, and he's happy with them.