PSVita day 1. Only console I ever bought at launch. Don't know why, but don't regret it. Xbox 360 was a couple months off of launch.

Original Xbox like 2 years late, is probably the longest before I bought one.

I still haven't bought a Wii, but never really had to because my housemates back in university days had it. So I funded the 360 and PS3 instead. So I guess that makes over 7 years and counting since launch?

Longest would be CD-i I got one in 2002 Call me crazy but I'm a sucker for FMV and it had the best video quality by far of it's generation.

The soonest would be the PS3 for me. I had one preordered so i got mine on launch day. The latest would be the PSOne since i got it when FF9 released just six months or so before the PS2 was released hehe.

Wii a week after launch
PS3 in 2011

3DS, one month after release. I wanted to play SSFIV 3D badly, and Starfox 64 3D would be releasing soon so I had to buy it early.

Bought the Xbox 360 on launch November 22nd, 2005

Bought a Nintendo DS on (insert month and date here) 2010

Bought a Dreamcast close to launch.
Bought a PS3 last year played it a long time before that over a friends house.

Nintendo 3DS. Got it a couple of months after launch even though none of the launch titles interested me. Playing the DS games with a circle pad while waiting for Ocarina of Time 3D to release wasn't too bad though.

Soonest: Gamecube, 2 months after release.
Longest: PS3, 5 years after launch

3ds 2 months after and ps3 in late 2011