The CX Amex and Citibank Premier Miles cards have each have their own advantage.

The Citi only gets access to the HKIA Premium Lounge near gate 40; it doesn't get access to the one near gate 15. However, supplementary cardholders do get access at the gate 40 lounge.

The Amex card comes with access to both the Plaza Premium lounges at HKIA and a free Priority Pass membership. But it doesn't come with access for the supplementary card holder.

And on the subject of overseas earning, I've just received an update from Amex that from 1 March 2009 overseas earning (double miles on the CX Amex Elite) means simply at merchants outside Hong Kong. This is better than Citi in two ways:
- Citi's "overseas" excludes the Mainland and Macau also
- and Citi specifies non-HKD transactions for overseas.

This reopens a nice opportunity for earning if you have transactions which can be done in HKD as native currency but outside Hong Kong. I benefited substantially from this in previous years when the old Citi CX card didn't have the non-HKD restriction.