Short films really do not have any marketability in my opinion. Unless you just want to do shorts. If you can take the time to write material for a 15-20 min short, put in the work to write a feature. People can diss Robert Rodriguez all they want but his advice is sound. Look around at what you have available, use that to your advantage. Shorts have their place, to gain experience, experimentation, promotion, etc. You can chase festivals, but the time and money you spend on trying to win an award you could have made a feature you could possibly sell.