DS - in 2005, now got 7 DS's =)
PSP - 2006 Bought 2, never played them until Crisis Core and Dissidia came out.
Wii - At launch, played it a lot. Now got 2 Wii's
360 - 2006, died twice but got it fixed. Been played a lot.
PS3 - Bought it at launch, waste of money. Nowhere near as good as the PS2. It died 2 years later and I still need to get it fixed =P
My most played consoles DS>Wii>360>PSP>PS3