Both?
Get the IHG card from Chase. $49 annual fee and lousy point earning (other than 5 points per dollar on IHG properties) BUT you get one free night certificate per year on renewal. It's pretty easy to get more value from the annual stay than the cost of the fee even if you toss the card in a sock drawer. IHG plat status comes with the card.
Same deal with the Hilton Reserve card from Citi, except that the annual fee is $95 and the free night requires $10,000 in annual spend AND is good for a weekend night only.
Both cards have nice sign-up point bonuses that can help with Europe, and both have no fees on foreign transactions. Overseas hotels for both IHG and Hilton (but especially Hilton) treat elites better than American properties.
If you want mid-tier status, you can get both IHG and Hilton with no effort thru credit cards. If you want top tier, there is not much difference between Hilton Gold and Hilton Diamond. See the Hilton thread for more info.
Mid-tier status at both hotels is so easy to obtain, I do both and just pick the better of the two chains according the city I visit. The trouble with chains other than IHG or Hilton is that I could never get enough stays at any of them to matter.