You can choose which ones depending on situaion, so those are natural both of "docchi" or "dochira". However, "dochira" is more politery than "docchi", so you can say "dochira" to your teacher, your boss and your older someone. "docchi" is more casuarl than "dochira", so you can say "docchi" to your friends and your family. And also, "docchi" is similar expression to "docchi no ho", so you don't almost have to mind how to use. Both of them are used about compared with something.

Exactly, "どっち" is more casual than "どちら". In addition,there is a regular phrase "どっち も どっち”. "どっち も どっち” means "They both have a point" or "There is no difference between the two" . I've not heard "どちら も どちら".