Chapter #87. "Sign up" Makes More Sense Than "Register"
"Sign up" and "join" feel more human and friendly than "register", which, to me, feels like something the user is being forced to do. Most of the time, the user doesn't want to sign up to yet another product—it's a frustrating extra step, another password to remember and another load of emails that they're going to receive.
Of course, there are a lot of reasons why the user needs to make an account, but don't call it "register": it feels unfriendly and "sign up" goes hand in hand with "sign in", which I recommend instead of "log in" (see #86, Use "Sign in" and "Sign out", Not "Log in" and "Log out").
Combining the Sign up control with some well-written messaging can really help the app to feel more friendly and useful. In the preceding example, we're recapping the benefits of creating an account to inform a user why they may want to sign up.