I have a Retroid 3+. It's amazing. I upgraded the sticks to hall effect and it's even better.
But after trying a Miyoo Mini, I'm never buying another Android retro handheld. The ability to turn on the device and play within 10 seconds is a huge difference. Even more important is that when you turn it off it goes idle and then powers down if you don't turn it back on in a few minutes. Android only goes idle on power off unless you explicitly pick shut down from the menu. Which means up to a minute between power on and playing. Without full power off you have to to keep it plugged in and charging or it will be dead in 3days of idle. Then there's the setup of emulators and front ends that takes time. Gaming shouldn't be a hassle and Android gaming is.