Friend is more informal while contact sounds more formal. I guess it depends of the application's targeted audience. Looking at the codebase friend is more used of the two. But it will be outright mistake to take this into account for a decision. The translators - me failing into this group - will be more than happy to use whichever term is decided upon as long it is used consistently.

Since you asked, my personal preference goes to "contact". It's elegant, does not imply any relation between the parties, overall fits better with the purpose of the application.

This has been a common point. I was convinced a while ago it should read contact, and not friend. The reason it's split is because I've only be slowly transitioning it over.