I will add my personal observation about nonrev benefits: between the seniority-based priority and aggressive overselling of barely-suitable aircraft for a particular flight segment, the benefits amount to very little as compared to other airlines (AA is one, but it could change post-merger). If you are a new hire, for example, you will pretty much be just hoping for a jumpseat.

United also seems to have a policy of upgrading almost every paying passenger to first class before putting a nonrev there. AA is much less liberal with its policy, as a counterpoint.