You're paying out a couple of grand, for goodness sake AUDITION, AUDITION, AUDITION!!!!!!!!!!
I'm sure (i'd hope) you wouldn't buy a car without first taking it for a test drive.
I'd guess though that the Pioneer would be my first choice probably- I have the LX81 (so last year) and have never regretted paying out the extra it cost over an Onkyo I first tried out. I had a Denon before that, and the Pioneer is more musical, controlled and altogether sweeter. The poise and control in multichannel is superb.
Though I haven't actually heard either system so I wouldn't like to advise you either way without that AUDITION! Not always easy, I know but I think you'd be a little loo loo not to.
Besides, you'll have a blast trying different systems. Remember, though, you don't need to stick with gear all from the same manufacturer. You may decide a Denon player sounds better with a Pioneer amp.
Whatever you decide on, good luck and have fun playing!