RPi4 and Pi 400 are the newer systems and the are faster than RPi3B. You can find a comparison graph with all models here : https://socialcompare.com/en/comparison/raspberrypi-models-comparison

I've owned The Raspberry Pi 3 B+ for a while and the Raspberry pi 4 4gb that I own right now is the one I prefer. If you do go with the RPI4 i do recommend you get heatsinks and a case with a small fan. If you are just doing non demanding emualtors then the RPI 3B should be fine. But with N64 I recommend the RPI4.

I do more PS1 and Dreamcast on my RPI4B and they run great. If you need tutorials check this channel out.

https://open.lbry.com/@Linux_Gaming:2?r=B6CR9WyDYNDMaAwhjpyCqZ7jRYdKhqcd