Here is my reply:
I have no personal experience with Behr, so I cannot offer any specific advice. Most of the professional painters I collaborate with use Ben Moore or Sherwin Williams. I think there is a reason for this, but I will defer to your painter for his answer.
What I can tell you is that when you invest in a professional painting job, the cost of materials is a small fraction of the overall budget. What you are paying for is the expertise of the applicator -- that is an excellent painter. So, to cut costs on materials can be a false economy. My rule of thumb is to buy the best quality paint you feel you can afford, that is also appropriate for the job at hand. For some people, that means a $125 gallon of European paint, for others it means a $15 gallon of Kilz from Wal-Mart. There is an appropriate context for both cans of paint, and everything in between.
When I discuss the materials investment with clients, we discuss the longevity issue. Are you moving soon or painting to sell? Do you like to choose new colors and repaint every few years just for fun? Are there children in the house who will likely outgrow their colors in the next 2-4 years? Or are you looking for reliable colors and durable paint that will satisfy you for a good number of years to come?
We also discuss wear and tear....kids, pets, high-traffic areas like entries and kitchens, etc. A certain brand of paint may be cheaper at the outset, but if it does not wear well and you need to repaint sooner, the savings is lost. This applies to the "big names" as well, where there are ranges of quality, from builder-grade paint (Eco-Spec) all the way up to the top of the line (Aura).
So, that is my take on the brand/quality/cost conversation. Hope this is helpful.