The only correct answer to this would be Atari 2600, which I also have, but, I'm not going to vote for that one. Because again, I'm biased in this. My vote is for the Odyssey2, which in Europe was called "Videopac G7000", with a Philips branding, because that name is more familiar here than that of subsidiary Magnavox;
Now, I played this system quite a bit, because even though I grew up in the early 90s, my mother had owned the G7000 since she was a kid herself so I played it as well when I was young. Some of my earliest gaming experiences are on this system. It's extremely simple, obviously, with one button, but it's controller's joystick was a bit more intuitive and fluent than the Atari's as it could move smoothly in all directions, instead of the stiffer 8-direction input of the 2600's controller. The controllers were hardwired though, so when about 10 years ago when I wanted to play some G7000 and I found one of the controllers was broken, I had to buy another system and take them apart to re-attach a new controller into my old system. The European version doesn't even have an on/off switch, it's just always on when it's plugged in and a game starts the moment you put in the cartridge. Talk about quick load times, modern systems can take a note from these old systems, but I eh I get it. Mine had one of those small lightswitches made onto the powercord, I think my grandfather did that, because I guess it being always on apparently didn't turn out to be that safe anyway. The system also has a keyboard on the front, but most games wouldn't use it. There's some games that included an overlay for the keyboard, like Game 42: Quest for the Rings, a D&D style RPG that also came with a board, chips and a booklet, where the keyboard had some use for extra functions.
In Europe the games were all numbered, from 1 to 60, plus there were a small handful of third party games like Frogger. In the end-of-the-year Top 50 thread, I highlight one game as my #50 entry in some years. This is Game 14: Gunfighter. In Europe, judging by the cover art because in-game you'll need some imagination, you're a gunslinger in the American west, having a shootout with another gunslinger. In the American release however, the setting of the artwork is more futuristic, and the game is called Showdown in 2100AD. Since single-player wasn't really invented yet, most games are multiplayer by default, and so was this one. All you can do is move across a field with trees to hide behind and shoot one bullet at a time, but it's actually a lot of fun and competitive to play something this simple against a friend. These things become quite intense. Most games are clones of Atari 2600 games, like Munchkin, which was basically Pac-Man; Space Monster, which was Space Invaders or Battle, which is Combat. Some of these came on a cartridge with multiple games. Also a lot of fun was the Basketball game, Game 6. It's even more primitive than the Atari Basketball game, and it makes no sense, but that's what's fun. An impressive one was Cosmic Conflict, which is like the old Star Wars Arcade game, it even has TIE Fighters, which featured a first person view and background stars and planets.
For the bonus, I'd say;
1. Game 14: Gunfighter
2. Game 6: Tenpin Bowling / Basketball
3. Game 11: Cosmic Conflict
4. Game 4: Air-Sea War / Battle
5. Game 20: Stone Sling
And no, I didn't remember all these numbers for the games, I looked them up. 
