The key thing to know is that flights determine the eye color of all your dragons!

http://flightrising.com/main.php?board=frd&id=704301&p=mb

Geeks tend to flock to Lightning; if you want to have access to spreadsheets of every possible fact and trend (and to help produce them!) join them. Otherwise, pick by eye color IMNSHO. (I'm Water, because I like blue. It's proven to be a mellow flight to be in.)