I think that it depends on the personality of the quilt you want to make. If you make a block, whatever size you determine you want to make:
If the strips are all the same width, then the quilt will have a more structured look.
If all the strips are of a random width, then you have a more scrappy look.
If you make the center strip all of the same width and the rest of the strips random widths, then you will have a structured scrappy look.
I've done them all different ways and all of them look different. My favorite is the center strip being the same width as I feel it gives your eye somewhere to rest, while all the other strips crazy sizes.
One thing I do try to do, however, is make my corner strips a little wider, so that when I cut the block down to the size I want, I don't little pieces of fabric left on the corner. If you have ever cut a strip block down to size before, you will know what I mean.