Short hair looks good on some girls, an bad on others. I recommend long hair because there are more things to do with it. For example: If you have long hair, there are many more hairstyles to choose from, guys love playing with long hair, you can do the hair flip, or hair twirl thing. Guys love that. And, it's more noticeable.
Some can pull it off. My old best friend had hair past his shoulders and his girlfriend barely needed to use a hairbrush; it was short. Talk about a role reversal. She looked decent enough to pull it off. I don't think too many can though.