I really think this is a worthy discussion in light of the upcoming Continental/UA merger since after Sept 2011, UA vs US Air will be the only two choices for U.S.-based *A FFP's. Let's compare/contrast in terms of:

1) Earning potential via flights on original carrier
2) Earning potential via flights on alliance partners
3) Earning potential via non-flights (Shopping Portal, partners, etc.)
4) Award redemption on original carrier
5) Award redemption on *A partners
6) Low/Mid/High tier status benefits