Is more expensive paint better?

Paint is the least expensive, yet the most important component of any painting project. That's why I always recommend using high quality paints. But is more expensive paint better?

Not necessarily. In some cases, the properties of the most expensive products would not only be wasted, but could be undesirable. I do recommend to avoid using the cheapest paints. They are inferior in quality. However, a reasonably priced paint when properly applied will undoubtedly outperform a top tier product that was applied incorrectly.
Last but not least, paint products undergo trends that effect prices. When suggesting a product for a particular project, I first consider it's technical data, and then price, presentation and fashion trends.
I've used many different products over the years, and continuously learn about and utilize new products as they become available. So, unless you have a strong preference, I will suggest the best material options to fit your purpose, style, budget and quality expectations.
Generally, I recommend to use:

100% acrylic paints for great lasting durability
Vinyl-acrylic latex for budget projects
Low VOC or 0% VOC paints for children's rooms and any projects where fumes are a concern
Oil-base or acrylic primers for exposed substrate
Acrylic and PVA primers for drywall surfaces
Shellac primers for glossy surfaces, exposed plaster and stain suppression
Stains, lacquers, sealers, varnishes and polyurethanes for emphasizing and protecting the natural beauty of wood

For best results, I use hand-crafted brushes, non-shed roller covers, fine finish spray tips and "top shelf" supplies.