As an artist I often wonder what size of a painting is best? I've read the thoughts of other artists and really its a toss up. There is no true measure of size that is better. I believe it comes down to the artist themselves.
Of late I have been painting smaller works on paper (see Paintings on Paper). I like the production time, lower cost to produce and mail. I read, "Smaller paintings doesn't take less talent just less wall space."
Years ago I was instructed by my brother Ron, a great artist in my eyes, to paint big. Big that will cover the wall above a couch. I have painted large pieces, well maybe not couch size, but 48"x48" and down. The only detriment to such large pieces is when I show my abstracts at art shows they are hard to fit in my "art mobile" and wall space in a 10'x10' tent is limited. For now my largest paintings are in the 20"x24" range.
I like to think that size doesn't matter to the patron looking to buy art, rather its the art itself. Size is not the object but content, design, colors, passion, what the eyes and heart see. With that I'll say, just paint whatever size you think is right ... just paint!