Definitely one of the newer Retroid devices. I have been playing on my RG405M but unfortunately the screen ratio and size makes it a bit of a challenge with some of the UI overlapping itself.

A Bluetooth controller or one of those telescoping ones though would probably be even better than that especially if you have a decent phone. I don't really use this method because the Bluetooth method feels a bit awkward and the telescoping controller involves removing my case which is annoying and it prevents me from using my phone while I play.