For me it's a draw between the 4th and 5th generations. If I had to choose though, I think I will go with 4th slightly ahead; the combination of FFIV-VI, Chrono Trigger, Secret of Mana, Zelda ALttP, Yoshi's Island and Super Metroid is a near impossible one to beat.
My least favourite was the 6th. While I love games like SSBMelee, Tales of Symphonia, Metroid Prime, Skies of Arcadia and Shadow of Colossus, with Zelda Wind Waker as my favourite ever game; I feel the 6th gen was a disappointing one. Possibly due to lack of competition by Sony/SEGA, the GBA was IMO inferior to DS or the PSP. SEGA left the hardware business. Finally, I can't really explain it too well, but I just feel that in the 6th gen Nintendo lost their way a little bit, thankfully finding it again in the 7th gen IMO.
7th is almost as not quite as bad as 6th. I argue that the DS has the best line up of any platform. Nintendo home consoles saw a vast improvement, IMO the Wii's library destroys that of the GC. My favourite genre, JRPGs, have IMO also improved almost across the board, the exceptions being Final Fantasy and Paper Mario. Despite this, it remains low on my list as I'm very disappointed by the two HD consoles, though the PS3 is seeing a rapid improvement IMO.
I haven't played enough of gens 1-3 to feel like I can make an accurate judgement and it is too early to say much about the 8th.
