Retroarch is more resource-intensive but it can run OK on New models. Sometimes its your only option like PS1 for instance.
I recommend Bubble2006k's emulators, the run well even on old3DS, although they have their limits. Mostly picodrive's less accurate and often desynchronized audio engine, so you can try Genesisplus GX on retroarch. mGBA is great for gameboy/color and some GBA games. The standalone handy for Lynx has some periodic sound bugs that the current retroarch version doesn't. Don't have much experience with other standalone emulators.