I have a few.
Kershaw: I used to love their knives, bought a lot of them. I was sharpening them a lot, then I bought a Buck Vantage Select with what was supposed to be a worse blade steel, and started to learn how important heat treat is for a blade. Bucks heat treat is phenomenal. Kershaw has a lot of nice designs but I'm just not that into sharpening. I don't necessarily hate Kershaw, but I haven't carried one in long enough I can't even remember. At least a year.
Buck: I love their heat treat. I hate their quality control and fit and finish. If I could get a Kershaw knife with a Bos heat treated Buck blade, it would be a great world.
Spyderco: Hated the ugly spyderhole and the way it ruined the lines of so many of their knives. Bought a dragonfly 2 salt and that just opened up the rabbit hole. Now I want a Native 5, no a Caly, no try the UKPK, what about a Manix... Domino maybe? yeah.
Rick Hinderer: I used to want an xm-18 soooo bad. It was my grail for quite a while. As I bought more knives, used them, even made a few, my tastes changed. Nothing wrong with his knives, just not my thing anymore. I think his collaborations with Kai may have cheapened his brand image with me a little as well.
Benchmade: I always thought some of their models would be OK if they were just a little less expensive. So much for that.