This is so very dependent not just on the individual cat but the circumstances as well.
I had 2 cats, bonded litter mates ex-ferals, indoor only. They were very close to each other, Boycat had a few "issues" (thick, clumsy, no attention span, no common sense, terrified of anything new) and his sister sort of looked after him e.g. took the lead on everything, always let him have first dibs at food & things (except Dreamies!). He was very cuddly indeed, she was more aloof.
At 8 he developed CKD & had to be PTS a few months later. She became incredibly clingy and needy. I usually work 4 days in office & 1 day WFH, she had clearly desperately missed me when I was in office and was so needy that WFH was almost impossible.
An only cat would have been fine I suppose if they could go out & meet local cats, but she'd been an indoor cat for nearly 7 years, there's a couple of VERY mean cats locally, and keeping her as indoor only was a condition of adoption. So I went out & found a young adult ex-stray male to keep her company, about 3 years old. He was very happy living with other cats at the rescue, especially females.
It's taken a bit of time, but they get on very well now. I've seen him licking her face and ears, they are always sleeping in the same room whether their own or mine and are starting to sleep closer & closer to each other on the bed, they play together etc. She is definitely the boss. The added bonus is though she's kept up with being more affectionate to me, she doesn't pester me non stop like the did when she was an only cat.
I would never have brought a kitten in for her company as I don't think she would have liked that. I was ideally looking for someone closer to her age but Tobias was there & he seemed just right. I wouldn't have taken a much older cat, as it wouldn't be fair on either me or Girlcat when they died, but if she'd been much older I would have looked at one nearer her age.
So to summarise, depends so much on the cat's nature, your circumstances, and the age of both the remaining cat & what you are looking to find as a companion.