On the information given I would lean towards a Pi4.
You have a ready made environment, a lot of documentation and many users which are in the same boat as you. The PS1 emulation works very well. Also Arcade games up to mid of 1990s will be fine.
You can also squeeze out a little bit more power if needed with overclocking.
With a Pi5, albeit having more horsepower, be prepared to learn RetroPie from the trenches. As you can see it this platform is still in frequent discussion here and there is no readymade image yet.
I started with a Pi3 my first arcade setup (as there was nothing else around), but I would not start with it again (in short: too many limitations for my requirements). If at all I would consider a PiZero2 which plays roughly in the same performance league but has a more modern graphics stack.