For me my favourite has been the RG34XX the GBA looking one. Due to nostalgia and the fact that I mostly play GBA games, but it works great for PS1 and SNES etc too.

I value silent buttons and a dim screen since I mostly play at night in bed beside my significant other and thankfully unlike most anbernics, this one is pretty silent compared to most. It could be better but manufacturers seem to not care about how silent or dim their handhelds can be so I often open up mine and mod them with foam and vinyl in specific places. Doing that to this one has made me pretty happy with it, whereas with my previous ones I never even really got close to what this one was like by default. Mostly thanks to them not using cheap clicky switches for the triggers.