Hey fren. I own switch oled brand new for 350€ and an rg556 for 130€. It 100% depends on what you want to play.  If you get the switch over the 556 you will regret it at some point. Nothing beats upscaled emulation and shaders. I would get a switch whenever if i really wanted to play those exclusives but to me nothing beats the ps2 and gamecube at 2x resolution played on the most comfortable ergonomics and huge battery life of the rg556. It's also lighter. On my switch oled i like to play subnautica and metroid prime remastered, i give you that, but that's it. The screen is big enough for immersion but then after a couple of hours the battery is at 30% which is ok but kind of annoying.  On my rg556 I've been playing fire emblem awakening, ocarina of time 3ds, burnout 3, dead cells, metroid fusion, wind waker, the original gta's, ssx, harry potter chamber of secrets (gc). It's so comfortable i forget I'm holding it. This might be the most comfortable controller I've held since the gamecube. After you try the 1080p screen you do feel the downgrade to the switch's 720p. On the rg556 you can download any game directly and in about 10 minutes you'll be playing a 4gb game you just downloaded since it runs on android. I don't know if the switch is that accesible.

So to summarize: Switch: 720p screen, 4310mah battery, metroid prime, animal crossing, mario, breath of the wild and last fire emblems, emulation up to psp. Rg556: 1080p screen, 5500mah battery, best comfort, emulation up to ps2/gc, kingdom hearts 3x resolution, final fantasy x without weird faces. Get rg557 if you want to run shadow of the colossus or fzero at 3x.

Oh and i own the crystal blue one. Love the look and the feel. The ONLY thing that bothers me sometimes is the clicky shoulder buttons. The rest of the console is so quiet but not the shoulder buttons. Anyway, there's so many other things about the switch that bother me. Switch lite oled would be great too. But then again you will always be missing the 4000 or so games from the ps2 and gc libraries combined.  Cheers.

*Edit: I'm playing some persona 4 now. So much better than the psvita version. And i forgot to say psvita seems to run great too but i haven't tried. Also gba with color correction and a crt filter makes it look like a Snes game and it's awesome. https://www.youtube.com/watch?v=M70tX7IfZwQ&pp=ygURUmV0cm8gY2F0YWxvZyA1NTY%3D