In many cases, picking only one game is practically impossible for me. So many made my childhood, not just one.
Gamebody Colour: Pokemon Gold. I lived off of this game. I took it everywhere with me, it was my bestfriend just in nuts and bolts and plastic.
Playstation 1: So many many great games. Including Crash Bandicoot 1, and Crash Bandicoot 2. Not to mention Spyro 1, Spyro 2 and Spyro 3. These two franchises, my god, kept me busy for hours. I can also remmber fondly playing Oddworld: Abe's Oddysee; so many good memories there two.
Playstation 2: Crash Bandicoot and the Wrath of Cortex, Spyro a Hero's Tale, Spyro Enter the Dragonfly, Grand Theft Auto: Vice City are the best games imo. Oh! I also can't forget about Ratchet and Clank: Up Your Arsenal. So much to do! The storyline was great. Everything about the game was simply epic. (Except for Dr Nefarious at the end who was SUPER hard!)
Playstation 3: FUS RO DAAAAAH; By far, by FAR Skyrim. It's got hours upon hours of content, the regions and missions are varied, and everyone's experience is unique. Absolutely stunning visually. It's definitely one of my favourite games, ever. 9.5/10.
PC: Probably Sims or Minecraft. These are really, the only two games I play frequently on the computer. I don't really like purchasing games for PC. Nevertheless, these are definitely the top of the bunch for me personally.
Nintendo DS Lite: Pokemon Pokemon and more Pokemon. Pokemon Diamond, Pokemon Heart Gold, Pokemon Mystery Dungeon, Pokemon Conquest. So many great Pokemon Games. Pokemon Ranger even! Now that I think about it, I primarily only play Pokemon games haha. Out of all of them, my favourite games would have to be Pokemon Heart Gold, based on its additions and nostalgic feel, as well as Pokemon Ranger Shadows of Almia. I loved the storyline.
PSP: I haven't played my PSP in aaages, but as far as I can remember I didn't purchase many games for it. I think my fav out of all the games I did purchase would probably be Ultimate Ghosts N' Goblins.