More to add to the United program:

Positives:
- Lots of airline partners.
- Star Alliance and Star Gold.

Negatives:
- No changes of any kind on many of their airline partners after departure.
- Rules for mileage accrual on code-share flights are very confusing. I wish they would just treat them like a UA flight just like most other airlines do.
- No elite bonus when travelling on alliance partners.