I usually buy fabric by the yard because it is cheaper, especially if it is on sale.
However, lately, I have been buying batiks in a roll because I can get a variety of different batiks in one roll and since batik fabric is so expensive, I can get a variety of fabrics for just a little bit more money.
As for fat quarters, I find that around here they are usually more expensive than the fabric by the yard. So, unless, I can't find what I am looking for in yardage, and it is just the perfect piece that I need, I will pass on fat quarters.