Tough call. The 80s had the Golden Age of Arcades as well as the rise of the NES, which was a historically important system (it single-handedly rebuilt the entire console market after the Crash of '83) that had a ton of amazing games released for it. Mario, Zelda, Metroid, Mega Man, Dragon Quest, and so many other amazing games and series were released on the NES. However, the NES didn't really start to take off in terms of popularity until 1987, as it wasn't even released nationwide in the U.S. until the fall of '86. The middle of the decade was a doldrums after the market crashed in '83. Arcades still kept things alive and kicking when the console market nearly died, though.
However, the 90s also had the 16-bit era, a period where we had the first and greatest "console war" ever. The SNES and Genesis arguably had more great games combined than the NES did. In many cases some Nintendo series, particularly Zelda and Metroid, experienced massive gameplay improvements in the jump from 8-bit to 16-bit. It was also the golden age of JRPGs, with classics like FFIV & VI, Chrono Trigger, Super Mario RPG, and Lunar. The NES was still getting great games in the early 90s, including the NA release of SMB3, my all-time favorite game. Arcades also remained popular going into the 90s, with the arcade scene getting a massive boost with the fighting game craze pioneered by Street Fighter II and Mortal Kombat. The middle of the decade saw the launch of the N64 and PS1, which also had their fair share of good games.
However, I found the last several years of the 90s to not be as good as those that preceded it. First off, arcades really started to go into a decline as the fighting game bubble burst and home consoles were able to match the graphical prowess of arcade machines. Speaking of the capabilities of home consoles, while the rise of 3D graphics opened up new opportunities to create new types of gaming experiences, few publishers seemed to grasp how to make good use of the third dimension, with many classic 2D series failing to make the jump to 3D and remain compelling gameplay experiences. Many games suffered from poor controls, muddy visuals, and terrible camera systems. Nintendo seemed to have the best overall ideas on how to transition to 3D, and they and Rare made some of the best games of that generation. Certain genres did make the transition relatively well, including JRPGs, which were either not really dependent gameplay-wise on being either 2D or 3D, and racing games, which were readily adaptable to 3D as they've been trying to fake 3D visuals for years. But many classic series like Mega Man, Sonic, and Castlevania all were hurt by attempts to transition to 3D. As a result, the N64 & PS1 simply didn't have enough good games as compared to the SNES and Genesis. Personally, I don't think we saw the industry as a whole really start to get a good grasp on how to make good 3D games until the 360 & PS3.
But as a whole decade, I'd probably have to give the edge to the 90s based solely on the sheer volume of good games, even if the majority of those were in the first half of the decade.
While my favorite decades where the 90s & 80s, I wanted to talk for a bit about the 00s and 10s.
As for the 00s, I felt they started weak and ended quite decently. The sixth generation is generally my least favorite post-'83 generation to date, but as I mentioned earlier I felt things really started to pick up with the 360 & PS3. Nintendo was kind of back-and-forth, that decade as, though they could still make some great games, they entered their current "gimmick phase," the negative effects of which wouldn't be fully felt until the current decade. The rise of online gaming last decade resulted in a mixed bag of good and bad things. On one hand the convenience and ability to play with a lot more people besides your friends was in many ways better than having to schedule LANs and lug systems around to them. However, the internet is filled with assholes who derive enjoyment from the suffering and misery of others, as countless victims of griefers and other assorted trolls can attest to. Digital downloads allowed for the rise of indie games and other small-scale titles, including re-releases of many old-school titles, that might not have been granted a physical release (though that's changing now, with some notable indies getting a disc release), plus it allows for easier distribution of expansion packs and other additional add-ons. But some of the effects of online-capable consoles some of which also wouldn't make themselves felt until the current decade.
That brings me to now. The current decade has had quite a few great games. The current generation has proven to be quite entertaining, and while there haven't been any great leaps forward, gaming has continued to mature as a medium. However, the current decade has also seen the logical consequences of some of things introduced in the previous decade. Nintendo's insistence on gimmicks was the downfall of the Wii U. While the system is great, with some of Nintendo's strongest releases ever, the system was hobbled by a poor gimmick that was not marketed well. They thought they could have lightning strike twice by going with an unconventional console again, and it blew up in their faces. The Wii U is the antithesis of the Wii in that it shows just how tenuous the commercial viability of gimmick-driven systems are, and that without that perfect storm of a good gimmick backed by slick marketing, the right games, and a sufficiently low price point, a non-standard console cannot succeed.
The mainstreaming of internet-capable consoles also has had its own fair share of issues, with perhaps more downsides than upsides. Online multiplayer has resulted in the steady decline of local MP support and "couch co-op," with some games not even having support for any local split-screen, and LAN support, if it exists, often isn't "true" LAN support as it has to run through the online servers. Currently, the only publisher that consistently supports local multiplayer is Nintendo. The ability to patch games post-release could save a potentially great title from being crippled by bugs and other issues, but at the same time it can incentivize developers to release incomplete games or titles that aren't properly tested and then fix them later. DLC, while once a promising means of extending the longevity of a title by offering new content without having to re-buy the whole game again (which we had to do back in the 90s whenever a Street Fighter or Mortal Kombat game got a roster update), has now been exploited by many publishers as a way of nickel-and-diming customers and otherwise gating off content that could have been in the initial release behind a paywall. Digital downloads might have allowed for the rise of indie games and the like, but it also resulted in full $60 AAA games coming out digitally, which, though still over an order of magnitude less popular than physical on consoles (according to a report from DFC Intelligence, physical outside digital for retail-release titles by a nearly 18-to-1 ratio in 2014, not including bundled copies), still normalizes the alienation of property from the consumer and threatens the possibility, however remote, of the very end of us owning the games we buy. The rise of online-only console games, including the expansion of MMOs and MMO-like games into the console space, also has troubling implications. Some games that could have been easily playable offline now have their very existence dependent on an internet connection, and one day your copy of such games will be rendered permanently unplayable. You know how aggravating it is not being able to play them when the PSN or XBL are down, or the publisher's servers are down? Imagine that, but permanent. Mandatory online was almost a thing for an entire system, but after public outcry MS backed down from their original online & DRM policies for the Xbox One.
While I feel that the general quality of games themselves has improved over the past 16 years, there's plenty of things that that I find disconcerting and make me worry about the future of what has been a lifelong hobby to me. The worst thing we had to worry about in the 90s was Nintendo censoring Mortal Kombat on the SNES. Other than that, I still think things in the 80s & 90s were overall better than they were now. It was a more exciting time, and the industry had yet to get too big for its britches, and the lack of online-capable consoles resulted in a paradigm where a game had to offer as complete of an experience as possible and be as polished and functional as possible at launch, plus local multiplayer and co-op had a social aspect that simply can't be replicated by online play. To this day, the NES and SNES remain my all-time favorite consoles, and the majority of my all-time favorite games were on those systems.