I prefer to use all original hardware, but I have no problem with emulation, as long as the important rules are not broken:
1) The emulator has to more or less correctly run the game. ZSNES-level accuracy is almost always good enough.
2) The display must not use a very obviously incorrect aspect ratio. I don't care about that Chrono Trigger moon or whatever, I'm talking about stretching from 4:3 to 16:9 (or worse).
3) The display must at least vaguely attempt to match what historical players would have seen. So none of those amazing but horrible smeary novelty shaders like in the "Lookin' good" image, and no drastic anachronistic increases in either display resolution or texture detail. But something like overclocking Star Fox is fine I guess, and widening a display area to modern aspect ratios (WITHOUT stretching) is also fine if it doesn't decrease difficulty or introduce too many nasty visual glitches.
4) The player must make at least a few earnest attempts at playing without cheating before resorting to heavy abuse of save states.
Pretty loose rules I think. I know some people on 4chan were really into maximizing resolution and clarity of early 3D games though, so probably #3 would lose some people who cannot understand why blurring the mathematically perfect edges of a 20-sided polygon that's meant to represent a racecar's tire might actually make the shape look far better than if absolutely every blade-sharp angle were perfectly visible in glorious 4k at 120 FPS.