I would say the Famicom Disk System.

Try getting your hands on the 64DD with a Japanese copy of F-Zero X and the DD64 cartridge that goes with it.
It may be worth a lot but it is definitely WORTH the space in your game collection.

BTW: SNES/SFC games.

Sadly I dislike the N64 greatly. I do not collect for the sake of collecting, I buy the stuff I plan to play.

Ah, well it was worth a try to ask, I kinda like the 64 IMO, not because of how horrible some of the controls were, it's more to do with the capabilities that the system had, Granted it had it's fair share of bad games.
On a side note:
I should tell you this and i must, it's so you know in case anyone even DARES to request this.
I will warn you about 1 thing about a specific Rareware game though, if anyone, and i mean ANYONE asks you to play
Donkey Kong Country 2: Diddys' Conquest, and mentions "Castle Crush" ignore it, it will SERIOUSLY brick the cartridge if done correctly.

Basically, what this basically is:
In the level Castle Crush.
The first DK barrel you come to with Diddy alone, when holding down and holding Y while holding the barrel.
Going to the very left wall, holding down and letting go of Y, then pressing Y again, causes Diddy to hold thin air.
Below a specific point in the level will you ever be treated with a glitch character, which will eventually crash the game.
There has been a case I've seen in one videos comment section, where the owners friend was playing, he accidentally bricked the game, and payed for a new one to replace it.

Anyway!
The crash, in some cases, will load some malicious arbitrary code, causing your save file to be a cause of a major error.
The code modifies your save file in such a way, by just going to the save select screen crashes the game immediately.
Thus meaning your cartridge is bricked and unusable by standard means.

I use a flash cart so any corrupt save data can just be deleted. As for bricking the actual game like that you can not do, the ROM's themselves are mask ROM's and can not be written to as they are not re-programmable. Any game crashing would have to come from a save file loaded into the games save ram and the game crashes when it tries to read it on boot. This can actually be fixed by disconnecting the battery. This clears the saved games out of RAM giving you a fresh blank slate to start with. This would fix any game suffering from corrupt save data. The Mask ROMS can become corrupt over time due to the chips themselves going bad but not from anything like this.

As for the N64 its not really the games or controller that make me hate it. The N64 employs terrible anti-aliasing which on a low resolution picture such as 240p/480i looks like complete garbage. I am a videophile and play all these old systems on a high end Sony BVM-14F5E in 15kz RGB. It and its 20 inch Brother are the two highest end CRT's available for these old game systems. Out of all the systems out there it has the worst video clarity out of all of them (Even the Atari 2600 can obtain a clearer video signal now through modwork). I do enjoy games like OoT and Mario 64 but the now high price of the new version of the flash cart coupled with the video problems the system suffers from (even with modded) has completely turned me off to it. It is probably the only game system I will emulate just because those two games work well on emulators if setup properly.

Another thing that bugged me was how LIMITED the vision was.
Playing Silence 2 (king league) even ON novice, I still had confusion on why I kept dying.
I just wonder, why didn't they stick with regular track instead of boarder-less roads, for that section.

Klonoa Door to Phantomile. PS1 classic it's amazing!