I don't think it matters which thread you use. I've been quilting for over 30 years using both; all the quilts have been washed many times and they're fine.
I'm a Bottom Line devotee
http://www.superiorthreads.com
I use Aurifil 50 as top thread when I need to use cotton; e.g., my Jems won't take BL on top if it's in the bobbin.