This is my all-time question. This time, I was writing specifications of my application and came up with this question. Which one of the following is more commonly used than the others? Note that I'm talking about a case without a relative pronoun.
When a user logs in for the first time, the user has 6 invitations remaining
When a user logs in for the first time, the one has 6 invitations remaining
When a user logs in for the first time, one has 6 invitations remaining
When a user logs in for the first time, he/she has 6 invitations remaining
When a user logs in for the first time, he has 6 invitations remaining
Or, any other suggestions to get the sentence more natural?