I feel I should speak up in favor of GameCube. It was a favorite in the poll but is taking a thrashing in the forum feedback here. Your mileage will of course vary with your hardware. I test on a Note 8 (with Gamevice), Note 9 (my primary phone), and GPD XD Plus.
This morning I fired up a few games on the N9.
Tales of Symphonia- sole transition hiccups aside, runs beautifully
Metal Gear Solid: The Twin Snakes- same as above.
Harvest Moon: A Wonderful Life- seems to run OK. Didn't delve too deep here.
Viewtfiul Joe- runs well, some frame rate drops here and there. The intro when the game first boots is bugged. Overall performance reminds me of playing Conker on Mupen64. Broken intro, very playable but not perfect game experience.
Fire Emblem: Path of Radiance- the opening story segment and cutscene played perfect. I have to go back and get into the actual game (don't shoote, its Easter, I'm trying haha).
Yu-Gi-Oh! The Falsebound Kingdom- as far as i can tell, just this side of perfect.
This is with no tweaking to settings on my end. It's about comparable to, say, playing PSP on my Note 8 was.
I haven't tested on my GPD yet, but I've seen videos of people with some tweaks running Wind Waker, Mario Sunshine, and Resident Evil well.
I know if you're on an older dedicated device and not looking to upgrade, this may seem unappealing. So I'm just voicing the perspective of people with recent hardware or who are likely to upgrade this year- this is far from the broken, unplayable hellscape the other comments are painting the picture of.
Also, to play Devils Advocate to the comment about marketing. I'm pushing 40, so not a young gamer. But I'm not sure the benefit we gain in visibility of the project pushing out C64 in 2019 INSTEAD of something that can run Twilight Princess and Metal Gear. Here's a link showing on newer hardware, Twilight Princess looks pretty darn good. https://youtu.be/-rEv47UaDIE