I'm currently 26. It's a bit of a read so for those who are TL;DR, my top 5:
1. SNES
2. Dreamcast
3. Gamecube
4. Nintendo DS
5. PSP
If you want to know why:
5. Playstation Portable - Second favorite handheld that not only introduced me to the hacking and modding scene, but had a rather impressive library to boot. Not to mention a plethora of Racing games like Ridge Racer, Gran Turismo, Flatout, and two excellent Wipeout games, Pure and Pulse.
4. Nintendo DS.
My favorite handheld, was my third handheld that I owned and the first one I bought on my own. Mario Kart DS is still to this day my favorite Mario Kart game for its single player mode and introducing me to the world of online multiplayer. The DS was also the first time I played an FPS online through Metroid Prime Hunters and was the first time I owned, played and beaten a mainline Pokemon game when I won a signed copy of Pokemon Platinum.
3. Nintendo GameCube
The GameCube is a console that I've somewhat recently realized how good it was and still is. I've always liked the design and feel of the controller since I was a kid and wished Nintendo or some other company would continue to use the features of like the analog triggers. Its library was on another level, though, as it had some of the best games from Nintendo and Sega including Smash Bros. Melee, Custom Robo, Super Monkey Ball 1 & 2, Metroid Prime 1 & 2, Kirby Air Ride, Mario Kart Double Dash and my favorite game of all time, F-Zero GX.
2. Dreamcast
Funny story about the Dreamcast, it was not only the first Sega console my family owned, but it was also then that I realized that Sega was a console maker, despite Sonic being my favorite character in media at the time. I had no idea about the Genesis, the Saturn or the Game Gear and I played three Sonic titles, CD, R, and 3 & Knuckles, all on PC, before finally owning Sega hardware for the first time. If nothing else, the Dreamcast became my entry point into Sega as a hadware maker and developer.
The Dreamcast itself was the first console I felt was a huge generational leap from what I was playing at the time. Games like Jet Set Radio, Sonic Adventure 1 & 2, and home console ports of games like Plasma Sword, MvC, and CvSNK 1 blew my mind from graphical fidelity to gameplay I didn't even think possible for a console at the time. Even smaller games like Re-Volt and Toy Soldier felt like third party hidden gems of games that only the SNES could match. Its a console I wish I spent more time playing and getting games as a kid cause had I played more of library, it would've been number one for me.
1. Super Nintendo Entertainment System
The first console I played to memory and the only one I have returned to constantly for good reason. It has the best library I've ever played. It pretty much had everything; even the games my family owned, like Super Metroid, Super Mario World, Cybernator, Mega Man X, SFII, ActRaiser, Super Bomberman 2, and TMNT IV just to name a few, still hold up today. Even long after we retired the SNES, thanks to stuff like the Virtual Console, I played and loved even more SNES classics for the first time like F-Zero, Pilotwings and Star Fox. Its the console that introduced me to the gaming world and what a hell of an introduction it was.