I've been painting for several years, have tried several brands. My very favorite interior paint is Bob Timberlake, made by the Coronado paint company. It is easy to apply (no spraying)and has more colorant than many other brands, even dark colors cover well with two coats. There is even a washable flat paint in that line. This runs $25-$30 per gallon. For a much more expensive paint that is great quality, you could use Pratt & Lambert. But, I see no reason to spend $10-$15 more a gallon. For a primer over the plaster walls, use Aqua Lock. Its very heavy-bodied, sticks to anything, even ceramic tile, and is thick enough to hide inconsistencies in your walls. Make sure to wash the walls first with TSP or another cleanser that etches the surface.