Yes, there is a difference in quality between paint brands and you tend to get what you pay for.  I've used Behr, Sherwin Williams, Valspar, and Benjamin Moore, and I think Benjamin Moore is the best.  It costs more, but  I think its worth it.  As for coats, I always use 2 coats even for paints that suggest single coat coverage.  If you've already cleared the furniture out of the room, spread a tarp and taped up all the trim and fixtures, why skimp on a second coat and increase the chance that you will have to touch up or redo the job later on?  It's not worth the hassle IMO.