What type of wire for dedicated 20A AC lines?

I’m about to have two 20A dedicated lines installed. What type of wire should I use? I know there are differences of opinion on whether to use 10 AWG or 12 AWG, however the link below makes a great case for using even 8 AWG solid core copper on longer runs like mine will be (50 ft), to ensure a lower resistance, lower voltage drop over the long run, and therefore more access to instantaneous current for my Gryphon Diablo 300. The wire would need to be stepped down to 10 AWG to connect with the receptacle. The article actually states that the thickness of the wire is more important than the fact that it is dedicated…

Assuming I want to follow this advice, which again makes sense to me, where would I find such wire to give to my electrician?