Nintendo. Their system exclusives are pretty consistent, and great. Not just Mario and Zelda, but Pokemon and Animal Crossing and all the other titles that capture your imagination. Have you tried the MySims games on other platforms? It's EA's attempt to rip off Animal Crossing and it lacks any of the magic or compulsion whatsoever.
Microsoft's exclusives? I loved Gears of War, I really enjoyed Halo, but they just aren't system sellers to me.
Sony's I have less experience of. I'd love to try Last of Us and all the recent output by Quantic Dream, but again, those aren't system sellers for me either.
Honestly? I've never clung to companies. Lots of them are out of touch with reality and just rely on their ridiculously loyal fanbases that refuse to accept that they're flawed. Remember the whole Valve paid mod fiasco? That was one of the happiest days of my life.