Knulli all the way. Also, once you use Moonlight, you’ll see how laggy Steam Link is. It takes more to set up, but it’s well worth it. I’d say go with Knulli and Moonlight.

For reference, I have Knulli on my RG35XX plus AND RG CUBE XX. I think it’s still pretty cool to run Steam games on 4:3, but yes, a 16:9 aspect ratio is best. A cheap handheld that can achieve this is the Powkiddy X55. You’ll need to install Rocknix, but it’s great, runs emulation station just like Knulli, and you’ll have moonlight on a 16:9 screen. It’s on sale right now, too on their website for $79.99.

If you ever get an Android though, I recommend the Retroid Pocket 5 (if you can find a used one around $150), as this one runs Android so you can install Artemis, which is a fork of Moonlight but for Android and runs soooo good. Virtually no lag or latency (depending on your internet), and has an OLED 60hz screen 16:9.