Hmmm... I do enjoy emulating gaming systems. But i also like virtual machines in general. Trying out a new linux distro without rebooting, seeing the latest features, running Linux and Windows at the same time and even sharing the same windowing space using VirtualBox addons... And then even systems that can be considered for gaming but just nostalgia with Atari800, Apple2 and trying older OSes, including Amiga.
And upcoming, with Risc-V becoming more a thing wanting to try out new chipsets and what a decent likelihood of systems that will be coming out once it matures enough to be viable (Also the likelihood of programming Risc-V chips to simulate other chips as it likely will take over as a cheaper replacement over other chips).
If i had to choose, it would be one that has simple enough features and was a good balance of performance, complexity, cost (hardware), and software i wanted to use. Probably non-3D (at least foreground stuff, background doesn't matter), unless it's after the Xbox/PS2 age where 3D was figured out enough to be really viable. I don't know.