A competently designed and implemented amp should be indistinguishable from any other competently designed and implemented amp in their operating ranges.
Not all amps are competently designed and implemented. Price is not a good indication; there are very cheap well-made amps and very expensive lousy amps, and vice-versa.
Here's a fairly recent comparison of two amps specifically chosen to highlight differences:
The frequency response delta graph shows differences of 5dB at many different ranges; an average person can reliably hear 3dB differences without training.
That said, the vast majority of speakers have frequency responses with much larger swings than many amps, and much higher distortion.
