Artists favorite question! So the short answer is calm colored abstracts, however that is only about 8% of sales and has the most competition. The truth is we sell mostly in the long tail, meaning we sell unique pieces, which makes sense given how subjective artwork is. So create what you love!
A few helpful actionable items I can tell you is that pieces smaller than 18x24 don’t sell as well and 20x30 to 24x36 sell the best.