Thanks for the pretty comprehensive advice.

I've had a look at the available properties in the locations I need and Hilton seems to be the most suitable from that perspective.

Starwood has an excellent stable of brands with a good range but unfortunately (as Raffles points out) not many of these appear to have much of a European presence.

Priority Club has better coverage this side of the pond but I've never been a big fan of Crowne Plaza and Holiday Inn while InterCon can be a bit pricey.

Hilton seems to be a good compromise for me and hopefully I should be able to make gold. More status to chase.