Super Metroid is fantastic. It's got amazing ambiance and it's ambitious as hell and all around great, but Megaman X is pretty much perfect. Super Metroid reaches farther and falls slightly short of its goals, its a bit flawed. Megaman X does exactly what it sets out to do.
The orignal Metroid, sure, I'll give you that. I've never beaten Metroid on the NES, but Super Metroid is 10 bajillion times easier. I never imagined someone would say that Mega Man X is easier than Super Metroid.