I dislike Sony because of last gen, being told to get a second job to afford that expensive PS3 at the time and then it breaking down a year and a half later which effectively caused me to move to 360 for most of last gen.
Dislike MS for charging online last gen and causing Sony to feel they can do the same, along with their horrid DRM E3 event which also gave Sony a free swipe and stab (seriously just as annoying) at the stat of the 8th gen.
Dislike Nintendo at the time of the Wii because it felt very casual and hardly interested me which also gave rise to the Wii mote along with Sony and MS trying to cash in on gimmicks which also irked me.
Dislike PC at times due to hardware issues that can crop up from nowhere, how Valve are a basic monopoly and anyone that seems to try are either destined to fail or be lauded as evil.
All in all I'll always dislike the fanbses the most though, I dislike pretty much all of them from master race, Sony,MS and Nintendo, they do more damage in my eyes and cause such trivial petty things such as trying to one up one another each generation and it's always the same and gets proper stale (this gen is no different at all).
That said I still like products from different corps, I'm grabbing a Wii U before Q3 and probably an XB1 at some stage (when they price down again or have a bundle I want), I can't say anything about a PS4 though, I've not been interested and still felt annoyed at having my 3 die after having paid for such an expensive product, I'll still always love games like Crash and MediEvil but I'd rather wait to see old ones return than see copied formulas all over again.