Scott- skinny 9 stone kid bro had a frame crack at the swingarm pivot weld, just out of warranty (the last 6 months being in a riding-free foot-and-mouth epidemic) and they told him where to go. Had some Scott spd shoes that fell to pieces quickly too. Wont touch a scott product again.
Trek, though I like the Remedy Ive always seen them as a souless megabrand (dont have an issue with Giant or Spec though…). Gary Fisher as I've never liked any of their bikes and hate the "inventor of MTBing" shctick.
Marin as I've never figured out what the point of them was. Fugly full sussers whos Mondeo like popularity drowned the market of individuality for a while, and worthy but forgetable hardtails overshadowed marketing-wise by the farm-gate full sussers. Not particularly rational but hey.
SSC purely on reputation here.
Continental after they seemed to stop putting rubber on the sidewalls and my XC's split after a few rides, many years ago.
I'm actually a bit conservative and loyal as a consumer, Ive always loved Konas but will happily admit that their spec/value balance plunged about 10 years ago, and they lost all small manufacturer nichey value when they went to halfords, and will always look at Camelbak as hydration pack of choice having been served well by them (still use my 1998 Havoc as my main riding pack). Only wear Giro lids etc.