Do you not have to use a corporate credit card for travel expenses? When I traveled for work we had to use the Corporate Amex or we'd get a stern email from finance.

Assuming you don't, I'd get a SPG or Hilton Amex and always stay in those hotels just to maximize miles.

Also as a clarification, I don't think the Amex Plat gives you HH Gold status. I think that was a limited term promotion and is no longer available. If I'm wrong, I'd be happy to know so I can call up and get that added to my account. I'm a lowly silver right now.