I prefer it to be a partnership. It is your quilt after all, and you are the one that has to live with it - it just comes to visit me for a short time ;-). I prefer to know your likes and dislikes (loose quilting vs. dense quilting, loves feathers vs. hates feathers, etc.). That being said, I'm supposed to be the 'expert' in the relationship, and I will try to gently guide you in a different direction if I think the design you choose will be inappropriate - perhaps flowers would not be the best choice if the quilt is for a teenaged boy, or the density is wrong for the batting we're using. Some things that are fairly easy to do on a domestic machine (SID for example) are much more difficult on a longarm. And if your seams are not straight and pressed every-which-way, SID would NOT be a good choice as it will point out the flaws rather than camoflage them.
It also depends upon the customer. Some do not want to think about the quilting design process, they just want me to get 'em done. Others want the input as that make the quilt more 'theirs'. So I try to work with you in the manner that suits you best.
Hope that helps!
Andi