I agree with the size recommendations you've received totally. As to brand...what I suggest is to go into a shop that has a variety of brands and varieties of fabrics. Pick out fabrics - lights; mediums; darks that you like. Grab a bunch of the different brand rulers and lay them over all of the fabrics. Which rulers do YOU see the markings best. Go with that brand. I also recommend, once you've chosen the brand of ruler you like - get all the different size rulers you want ALL THE SAME BRAND. An inch is not necessarily an inch when switching from brand to brand of rulers. Has the potential to affect your cutting accuracy if you change ruler sizes mid way through your project.
Just my 2 cents.