Must I whittle my list down to just 1? That's making it far too difficult
Most in alphabetical order even! Only with a few at the top that are really high on my noooooo list.
Peugeot (worst brand of car I know of, worst build quality I have ever seen & even brand new they fall apart as soon as you leave the showroom... I might make a small exception for a 205GTI, can't believe they went so bad after making such a good car, even if it was more than 30 years ago)
Kia
Skoda
Range Rover (ok, I know that's not the brand... I just really strongly dislike them... but there is a possibility of having a proper Landy at some point)
Audi
Renault (perhaps with the exception of one of their purpose built race cars, they seem to kick out some poor road cars, but their race division comes out with some nice things)
Citroen
Fiat
Bowler
Bugatti (might be special, quick in a straight line and whatever else, but their heavy weight, no matter any clever suspension management of it, will make them unfulfilling in the twisties & that is where the fun of driving is for me... planting your foot in a straight line gets old, fast. Mastering corner entry, mid and exit speeds are where the fun is)
Caterham (I had one, a quick one and I found it bore me too quickly, didn't have longevity of the fun factor for me. Others love them and they are cool and quick cars, the standard width chassis being more enjoyable and playful than the SV, just not something that interests me any more)
Chrysler (they make such terrible vehicles, I'm not sure how they are still in business, although for some reason my mum is very fond of her convertible PT Cruiser... at least the convertible doesn't look quite as much like a hearse as the coupe)
Dacia
Daewoo
Daihatsu
Delorean
Hummer
Hyundai
Infiniti
Isuzu
Jeep
Lada
MG
Mini (modern Bini)
Mitsubishi
Morgan
Morris
Plymouth
Pontiac
Rover
Seat
Smart
Ssangyong
Subaru
Suzuki (cars only, they make great bikes)
Tesla (not the biggest fan of the feeling the power delivery gives you, from even the insane mode variant, it's weird - you know it's fast - unusually fast for a heavy saloon... just with such a flat torque curve, other than the very first throttle press, it doesn't feel quick and excite with the feeling of the acceleration, you just go quickly and know you're going quickly, but there's no life to it. To be a fair to the saloon, the chassis setup along with it's handling ability and feeling/communication back to the driver for such a heavy car impressed me. This entry on my list though, is more of a severe personal dislike for Elon Musk... I will give them some credit though, the way they have pushed the development of the electric car & deployed such a comprehensive matrix of fast charging stations over a wide footprint is commendable & the timeline they expanded that footprint was rather impressive, even if it was a vital requirement to make their vehicles somewhat viable to your typical motorist who has to take the odd journey past its range or didn't have the time or perhaps ability to top up the charge enough at home... even if recent financial troubles may indicate it's not the most financially viable business model... plus the unfavourably large number of reports of them voiding warranties and lumping massive repair bills on their customers is unacceptable business practice. Also, the new roadster that's coming in a few years looks to be an impressive leap forward in both acceleration and range)
Triumph
VW
Volvo
Honda would have made the list if they hadn't managed to kick out two incredible vehicles... the original NSX & S2000, both of which I would love to own some day.
Mazda too, but they make one of my most favourite cars ever - the MX5... the RX8 wasn't horrible either with a well balanced chassis & the modified RX7s are a welcome sight and sound.
Reliant is purposefully not on the list, because sticking a roll cage in one and doing a top gear on private land would be hilarious!
Toyota is another one that I'd have liked to stick on the list, again for their wide range of uninspiring standard models, but they have made some incredible vehicles in their time... like the MK1 & MK2 MR2 (I'll let them off for the MK3 because the first two are so good), Supra and Celica (especially the rally variant).
TMI?

Was good to vent my frustrations of unfavourable marques
Vauxhall.
Substandard vehicles and in my experience driven by council estate failed abortions. Oh an I also have no desire to sleep with family members, animals or children.
I was almost tempted to agree with that, given the majority of the vehicles they churn out... but then I remembered the VX220, Monaro, VXR8 and the latest VXR8 GTS.
The VX220 hasn't really taken my fancy, but it still looks like a bit of fun if you fancy something a little different.
The near 600bhp from the latest iteration of the supercharged 6.2l v8 VXR8 GTS sounds like a fun prospect for a saloon & makes some great noises... only downside is you have to put up with the Vauxhall interior :/ I haven't had the chance to play with one yet, but one possible downside is I hear they don't manage their weight as well as you might hope & tend towards understeer (which is always frustrating, especially in a powerful RWD car).
/long long ramble over