SNES/SFC (double edged sword, amazing game library but the hardware itself leaves a lot to be desired, hate the slowdowns and general slowness of many games, also not the best soundchip)
That's almost exactly how I feel about the SNES, except I find myself not wanting to play it just because of the flaws you state.
Since I am mostly into shooters, I usually go for PCE or Genesis, then go for the NES for action platformers. Still, with games like Super Metroid, Mega Man X, Actraiser, Final Fantasy III and Super Ghouls and Ghosts, it's hard for me not to keep it around. It just always feels a bit sluggish to me, so I prefer the crispness of the PCE or even the NES.
With that said, I like the PCE, Genesis, NES and Neo Geo almost equally, with the SNES closely behind, so as long as I can keep those, along with one modern console (either 360 or PS3), I'd probably be happy.