Of course, any short haul holiday the answer is 10 days, but with this not really widely available in a package set up (aware you can do your own thing), which do you prefer? I love day six of a holiday and you're all relaxed ready to go home.
The idea of staying for two weeks strikes me is a little bit boring but I am very easily bored.
I think in my six week teacher holidays, I'd rather do two weeks of holiday/activities/trips rather than one solid two weeks stretch.
(I haven't got any kids at home anymore.)