The short answer to this question is "whatever you grew up playing."
My all-time favorite would be the Atari 8-bit home computers. I had the 800XL for many years, which was the most popular model. My grandfather later upgraded to the 130XE, which had that extra memory that was sadly never used, and a casing design that looks nice but was actually much cheaper quality, especially the keyboard. Gotta love the Tramiel Clan's ability to stretch a buck.
Anyway, the Atari was my favorite and remains so today. It's the best for the "golden age" arcade videogames, features lots of terrific original and groundbreaking software titles, there's a million indie/homebrew games created by bedroom coders, lots of very good application software (I used Atari Writer all through high school in 1991). The only thing the XL/XE is missing is four joystick ports so that you can play 4P MULE, which is probably the greatest videogame ever made. Oh, well, you can always use the original Atari 800 for that, or build a circuit board for extra joystick ports (the late, great Raster posted the schematic online years ago).
The only reason I wouldn't list Commodore 64, Amiga or ST is because I didn't have any of those computers, but they're fantastic for games. The Amiga has to be the greatest of them all, but C64 has that glorious SID chip, and don't discount the Atari ST line. A 1040STe or Mega STe makes for a damn good computer for its time.
The best dedicated console? That's trickier. I'm almost required to say NES was the best, as it revived a dead industry in the States and its software library has something for everyone. The Sega Genesis is a pretty strong contender thanks to its excellent 2D platformers, shoot-em-ups and sports games. It has NHL94, the greatest sports videogame of all time, as well as Sonic, Streets of Rage, Capcom, Disney and Technosoft. The Atari Lynx remains a beloved favorite thanks to its Epyx and arcade titles, especially the Atari Games hits. The tech on that handheld was decades ahead of the curve, and when it comes to 3D graphics, you'd have to wait for Playstation Portable to finally surpass it.
All that said, when I want to play videogames these days, it's no contest. I'm reaching for the Sega Saturn. It's the Velvet Underground of videogames.
P.S. Oops, completely forgot about the Nintendo Wii, another one of those systems with a seemingly endless supply of hidden gems and surprises. The best part is that so many games are available for five bucks or less these days. I just got a Switch for the family this Christmas, so it's too soon for comparisons, but I do think the Wii did everything just a little bit better. It's worth it for the Wii Series, Just Dance, Mario Galaxy, New Super Mario Wii, NBA Jam and NHL Slapshot.