It has to be the 2000s by a mile. If you look back, there were really only three or four years in the 90s that were any good. 1992 was the best year of the decade, and 1994, 1996 and 1997 all had consistently good matches from Bret and HBK, but the rest of the time it was pretty crappy.
The best year this decade (2000) trumps the best year of the 90s (1992), the really good wrestling has been better this decade than last, and there hasn't been one year where match quality just completely bottomed out like it did in 1990 or 1995.