Better quality paint means you will paint fewer times over the years, and you'll get better coverage when you do paint. Paint technology has improved dramatically in the past few years, with colors guaranteed to last longer than ever before. You may be tempted to skimp on paint to save money up front with a cheaper brand, but you're bound to have trouble and eventually pay more in the long run.
The rule of thumb has always been to apply a good coat of primer, sand, then apply your color coats. This is still a good rule to follow, but new paint technologies have combined primer and paint into one product, which manufacturers assert will cut down on the number of coats you will have to apply. This newer paint is more expensive, but may be comparable to the purchase of separate primer and paint. Look at reviews of these newer paints, particular from folks that have used it in your area. House Painting Westminster