Streaming: WiFi or wired??

Mahler123 is right.

Both wired & wireless will work excellent as long as they are working within their limits. The chances of wireless dropping packets and causing re transmissions are a bit higher than wired, especially if a lot of wifi devices are sharing the same band. Moving to the 11ac at 5G bandwidth may reduce those issues, unless you live near an airport or anywhere where radar signals are present.  This may cause the AP to change bands continuously (DFS).  Also, with higher frequencies (at 5G) , your signal degrades quicker so distance becomes more of an issue.  This is laws of physics and you just have to live with it.

99.999 % of the time, both will be fine :-) It is really a choice of convenience.

In this thread, I have read some references being made to "noise" in the PSUs and/or wifi signals. This is completely irrelevant.  The wifi signals (and hence the audio signals in the data packets) are carried in a digitized way and the PSU noise of the wifi and/or wired AP has ABSOLUTELY NOTHING to do with the quality of the analog signal you will achieve after it has passed thru your DAC.   Any AP noise issues will be automatically taken care of by re transmissions and CRC checks and error correction algorithms.

Wifi is more than adequately fast for even the highest sampled digital music, unless you have an ancient AP router older than about 6 years.