Depends on the age.
I like a new owner every 1-2 years, so a 6 year old car with the first owner for 2 or 3 years and then a new owner every 12 months or so is fine.
I have always found the cars I have bought with a few owners have been in better condition, I am not saying that single or 2 owner cars are not looked after as well, just that I think you don't notice the little squeaks, the odd knock, or slight creak when it arrives over time.
Get a new car and you tend to sort out all those little niggles as you want it to be perfect, you always give a new car slightly more love that something you have had for 3 or 4 years and want to move on.
Obviously if a car is 3 years old and had 6 owners already you have to wonder why?