Anytime you use a fleece it is going to pill.
Be that you are using it for a garment or a quilt, it will eventually pill.
The length of time, I believe, before it starts to do this is in the washing and use of the fabric.
I have used fleece for two quilt backs and one pilled faster than the other but I think it is because one was used/washed more.
Doesn't matter to me.
I love flannel and fleece so I will use both for applications I deem it worthwhile.
Hope this helps.
Kirsten