I got back from London yesterday. My analysis of the IC Park Lane and Kimpton Fitzroy as an IHG Spire Elite may be found here:
https://www.flyertalk.com/forum/31063971-post6.html
Club access at The Churchill was lovely, as always, but we were assigned a lousy room.
As a Hilton Diamond, I would just stay at the Conrad and enjoy the top-tier benefits. As for location, being near a Tube station is nice, but I'm finding using the public buses to be even more useful for getting places within London, especially in that I can use my iPhone to pay for the fares.