hmm.. This is a hard one for me. I have always loved what Nintendo put out. If I had to choose one console they completely failed on, it would be the Virtual Boy, but thats not one of my options in this thread.
I love the N64, as a matter of fact, I had pre-ordered mine and waited in line on launch day to get it along with Super Mario 64, which I also loved a lot!! I was a little disappointed they decided to stay with the cart format, but hey..I still enjoyed the system, and still do from time to time.
The Gamecube....hmm... another awesome console, IMO. Super Mario Sunshine was certainly a different way to do a Mario game, but I thought it was genius! I put a lot of hours cursing, throwing tantrums, ect..into this game. The Zelda series on this console was also one of the reasons I actually bought the system. Windwaker was IMO one of the best games in the series. I loved how they did something, different.
Now, my Wii... Although I do enjoy my Wii, it is the least favorite of the Nintendo consoles for me. I realize the Wii wasnt made for power, and I have no beef with that. My thing is the amount of crap games compared to the amount of decent games out for this system. The small handful of games I have bought for this I have enjoyed, such as the Zelda series and Super Mario Galaxy. However, if it wasnt for the ability to play Gamecube games, and the ability to download for the Virtual Console, I wouldnt really use it. I also use it for NetFlix, but thats another story. It does have its uses. I can download my Final Fantasy II and III for SNES and not have to worry about battery back-up on the cart. Up till I started buying heavily in the TG-16 library, I was grabbing those as well. My Wii is actually fired up more than my Xbox 360!! For the price, and what it has to offer, I think its done its job.