Priority Club is great for getting lots of free rooms, but they are highly variable as to room quality and a platinum is treated about the same as the guy off the street.

Starwood has a great program but no hotels except in major cities. So if your travel is limited to big cities it is a great choice.

Marriott is right between Starwood and Hilton in that it is in all the big cities plus a few smaller towns. Nice elite benefits.

I don't travel much anymore, but my wife does and I tell her where to stay (sort of). Hampton Inns are everywhere. So it's easy for her to keep her Diamond status.

So decide what you want to do and do it. My wife stays enough at Hilton to keep Diamond, enough at Priority Club to keep platinum, and then tries to take advantage of as many offers as everyone else has, such as Marriott Megabonus, to earn free rooms. You have to decide what's best for you, but I assure you that after you stay at enough Marriotts or enough Starwoods you'll have some bad experiences. I booked my wife in one Starwood which turned out badly and she refuses to do business with any of them, even though it's a great chain.

The year is half finished, so I would assume you have nearly 15 to 20 Hilton stays. I suggest going ahead and making Diamond for next year while picking another chain that you'd like to romance a bit. If things don't work out, you'll still have your HH diamond, which will come in handy when cashing in your remaining points.