I've always felt that Oneplus is a brand that I should like on principle of having clean software with barebones but powerful hardware, but in reality, every single Oneplus phone I've seen always had some sort of big BUTs attached to them, so buying Oneplus always feels like settling.
Take the Oneplus One for example, that sandstone textured cover was THE most creative material I felt a phone could have had, and I'm honestly shocked nobody has ever done it again. But along with that of course, comes with the cringy "smash your phone" marketing campaign, the half-hearted attempt to distance themselves from their parent company Oppo, the whole software mess with CyanogenMod/OxygenOS, etc.
Had a Oneplus 3T for a while, same deal: Great phone when it works as intended, but they raised their price without making the phone better, and the inexplicable random restarts/battery drain is so irritating, never had another phone that does that.
Recently they've dropped all pretense of not being Oppo and abandoned their core audience, choosing to have the "courage" to drop the headphone jack. Mediocre Chinese phones with flagship specs are a dime a dozen, I just don't see a reason to buy them anymore.
Used to be high spec and a low price. Now they're average spec and an above-average price.
Nowadays phones are all pretty similar in price and spec, so I'd rather get a slightly more expensive phone from a company with proven, accessible warranty.
All tech is great when it works all the time. The problem is what happens when it stops working. Can you contact them? Where do you send it for repair? How long does that take? All that sort of thing.
I had a OnePlus 3 for awhile and gave it to my daughter, who broke the screen. I contacted OnePlus and arranged a repair, and got the battery replaced at the same time. I don't remember the price but it seemed fair at the time and the turnaround was about 2 weeks.
I have a Samsung at the moment and have had Samsung's for 6 or 7 years. I've only had minor issues with a few of them, and I've been able to visit a Samsung retailer / service centre to actually get them looked at in person.
So, proven reliability for my experience and ability to get it looked at in person is something that means I'm happy to pay more for the phone than I would be for other brands.