For grisette, I have been using the Thiriez yeast, cultured from a bottle, and I like it quite a bit . Otherwise I am partial to a blend of 3711/3724 (favoring the 3724) if you want to go in more saison yeast-driven route . If you don't want to go this way, I like Wyeast 3787 fermented cool for beers of this nature . Those are just some ideas, and you should use either your favorite saison yeast or blend, or your favorite more neutral Belgian ale yeast.