Maybe asking which is best isn’t the right way to word it but anyway…
I just tried out FCEUmm and then nestopia. They seem equally good but I noticed save states aren’t interchangeable and I would hate to choose a core that has an issue turn up later.
Same goes with the snes cores. I assume SNES9x next is probably the best simply because it says “next” but I’m not sure. There must be a reason multiple cores are included and supported. I know there is also the new bsnes included as well but that has audio issues in the super Mario rpg which I figured could happen in that core with certain games.