I prefer doing. Assuming that what I do is worthwhile. I believe that being is not enough for me personally. I am here for a reason and while I may not know what that reason is, I will be damned if I am not prepared.
All this is clearly relative. Some see doing as a way of being. Some see being as a way of doing. Some see both as mutually inclusive. It all depends on how you look at it, or look at yourself as a person. Do you do because you are? or do you do because you want to be? It can also be both, as some of you said.