Shag, welcome back. Of the units that you're considering I'd definitely suggest the Denon X4200W. Although in previous years I most often gave Onkyo an edge over a comparable Denon model, this changed when Onkyo downgraded their room correction processing from Audyssey to a cheaper and less advanced in-house AccuEQ system.
The NR757 doesn't have the same feature set and power as the X4200W. The X4200W features the highest grade Audyssey MultEQ XT32. Also note that the 180 watt number sometimes seen in advertising for the NR757 isn't an "official" power rating under the legally required FTC amplifier regulations. That number is at 6 rather than 8 ohms, at 1KHz rather than 20-20KHz, and with only 1 channel rather than two driven. The FTC number is 110 watts. The FTC rating for the X4200W is 125 watts.
An excellent buy for the X4200W is the factory refurb(which, if anything, should be even more reliable than a brand new unit)from
Accessories4less for about $900.
