The best fabric to use is one with lots and lots of motion and several colors. 12 to 24 in repeats are the most bang for the buck... you will get a bigger quilt out of a 24 inch repeat.
If you are shopping on line and can't tell the repeat size send and email most companies will get back to you on the repeat size.
Hancock-paducah and equilter.com have done this for me on several occassions.
You can also go to a home improvement store and get two piecse of glass cut and use duct tape to put them together to make the "special mirror" that is sold to tell if the fabric will work well.
Good luck they are very beatiful quilts when done.