It's tough for me to say, I never really owned a Nintendo. I did just buy a GameCube, but I have never played it. My sister uses it for Harvest Moon games.
My first console was the Genesis, second console was the PSX.
I have an Xbox, and if the xBox360 was as open for hacking then I for sure would have put xbox (I guess they want you to have a bunch of Media Center PC's running Vista just to use it as a media center, but I call bull and say that it should be an open system.)
I have a Dreamcast and love the VGA output, but sadly the controllers ruin it for me, and so do the $20 apiece PSX to Dreamcast adapters, what a rip-off. Sega doesn't seem to grasp ergonomic controls.
Sony has an interesting cycle of releasing units with crap optical drives and tons of special processors that never get used. Then shrinking the whole unit and selling it for a few more years.
I am afraid the PC is the ultimate for me, simply because I can't stand closed software systems. The hardware is just begging to be let loose, and why can't it be? Why do we have to be saddled with whatever will sell to the lowest common denominator?
PS3 with Linux was an interesting turn, but a Geforce 7900 series?? Come on, you can get those for $45, it isn't really worth it. A Q6600 is only $190, put those together and not only can you run a ton of PC games (even more if you are smarter and choose a ~$100 8800/9600 card, or better yet ~$175 and get an HD4850).
So I chose Sega, simply because they can really make a game. And they had some of the neatest portables first.