InvisionFree is good no matter what others say. At least you can change the look of the board and add cool hacks/codes/scripts easily and without having to replace files and all that crap.
And it is a big community, with many people, many skins and graphics available too.
So yeah, free services are a good choice, too. The only ads in Invisionfree are the google ads and that's all. No annoying popups and it's fun.