I'm honestly fine going either Casual or Free.

I just tend to avoid free because people there usually just don't illustrate character development or personality well.
Like one example of an RP I backed out of before actually joining, people had stuff such as getting bitten by a vampire and then just walking to class like them being mysteriously gagged, attacked and turned into a monster was some kind of everyday thing, and was meta-game galore (As in all characters seemed to start off with every bit of background knowledge provided in people's CS's). Casual at least has people who consistently come up with decent plots and ways to flesh out characters.

Basically, I don't much care for post length one way or the other. Just as long as the plot has a decent pace and we actually remember to treat characters as actual characters.