Among those, you should buy based on desired features. Other than engaging a circuit that affects the sound (e.g., proprietary DSP modes), they will all sound the same with any speaker that they can adequately drive.
I would say that the Pioneer Elite VSX-31 is sufficient, if it has all the features you require.
Whenever you want better sound, look to better speakers (including subwoofers) and room treatments. Except, of course, when one's amplifier is inadequate to drive one's speakers (in which case, the best option is typically to buy a separate power amplifier and use preamp outputs from the receiver, instead of buying a more expensive receiver). Otherwise, any receiver or amplifier from a reputable company will be fine.
A common mistake that people make (if sound quality is what matters to them) is to spend too much on electronics, and not enough on speakers.
In my case, I am currently running a receiver that retails for about $1700 with speakers that retail for well over $6000. Previously, I was using a receiver that retailed for $600 with the same speakers. It sounds the same as before, unless I engage a feature that affects the sound. (I bought the more expensive receiver because I wanted more features; I also got it for less than 1/3 retail price, as it was a discontinued model.) If the best sound quality is the goal, one should buy a receiver from a reputable company (e.g., Yamaha, Denon, Marantz, Pioneer) that is about as inexpensive as it can be while having all of the features one needs, and then spend one's money on the speakers (speakers, of course, include subwoofers).
