Cakyol has his head on completely straight and seems to be grounded in the laws of physics. I use 24 gauge wire for one of my systems with a 3.5 watt tube amp and high sensitivity vintage (Frazier) speakers - it sounds incredible, top to bottom. Generally for higher output, I would personally go with a larger gauge - BUT nothing fancy or expensive. I have been very happy with the high quality, flexible Installgear wire from Amazon (Cakyol’s second link) on my main system (a more beefy McIntosh tube system). A friend of mine with 40+ years experience and some of the best sounding gear you're ever heard, goes with 14 gauge wire from Home Depot. Hell, if it was good enough for the iconic Paul Klipsch, that's good enough for me.
williewonka, and several other of these bloviators for that matter, on the other hand are marinating in snake oil. PLEASE don’t get sucked into the "cable science" nonsense (non-science)! All auditory hallucination paid for with obscene amounts of money and bolstered by clever marketing designed to steal your cash. And don’t bother to argue with them - predictably, they’ll now attack my system, hearing, sophistication, credibility, etc, with zero science to back up anything they try to put forth. Just put them on mute, move on, and enjoy the MUSIC.