Small group is fun, especially if they share your ethos about wild spaces and enjoy making the best of it. That said I'd rather know them to some degree, there is absolutely nothing worse than having a whinger along for the ride who repeatedly has a good moan about how it's all 'so hard' or complains about the route, yet never gives any time or opinions on it prior to setting off. Also when the weather is truly shocking a small group is more fun than solo, there's a bit of camaraderie in adversity thing going on when you're wet through and struggling to make progress, a few positive comments go a long way to keeping morale up, whereas when I'm solo I'm usually wondering why the hell I decided to spend my day walking through clag.
Usually I prefer solo, I'm a quick walker and I enjoy seeing as much as I can on trips, often descending with a headtorch after a full day out. I don't have an extra long lunch stop or take many breaks, I'd rather be flying up something and down the other side and put that time into getting back to enjoy a pint or decent meal outdoors at a pub, especially if I get to watch a sunset a the end of the day.