Nintendo - mainly cause of their first party titles such as Mario, Pokemon, Zelda, Kirby, Donkey Kong, Smash Bros and Mario Kart. There's some other titles and IPs that I like but those are mainly my reasons to love them.
Edit: oops Nintendo dev eh........I guess EAD, HAL and GameFreak, too hard to choose ;x.
Most favorite titles include
-Super Mario World
-Super Mario Bros. 3
-Super Mario Galaxy 1/2
-Super Smash Bros Melee/Brawl
-Mario Kart DS/Wii
-Kirby's Super Star/Ultra
-Donkey Kong Country 1,2,3
-The Legend of Zelda Twilight Princess/Link to the Past/Ocarina of Time/Link's Awakening
-Pokemon G/S/C , R/S/E and B1/W1