If you didn't need award travel worldwide I'd also suggest looking into America West. You'd get to know Phoenix pretty well, but you'd also rack up points and their elites get upgraded nicely. With HP your partner redemption options are limited but do include BA.

Otherwise, seriously consider AS.

Their program is truly top notch. Earn status miles (no upgrades) on CO, AA. Earn status miles with some limited upgrade ability on NW. Redeem on those, plus Cathay Pacific and Qantas.

MVP Golds are treated very nicely, including the ability to confirm upgrades on AS metal at time of booking, subject to availability, regardless of fare.

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View from the Wing: A blog about Free Miles and Free Markets