The dilemma is that the hotel programs where it's easy to get lots of points from card signups don't have such good locations and/or values (at least in Rome), and the hotel programs that do have decent locaitons and values don't have much of a credit card signup (such as Choice).

Choice is a great deal often if you stay in cheap suburban hotels and then redeem for much nicer hotels in Europe. And with constant promos like 4x points (ending tonight) or stay 4 cheap one-night stays in the US and earn enough points for 1 to 2 nights in European cities, you earn points really fast if you stay at Choice often enough, without big spend necessary.

However, the Choice card does not earn very well (outside of Choice stays), and the bonus is only enough for a couple nights in Europe. Also, unless you have status at Choice, you can only book (European hotels for a US-based traveler) about 2 months in advance. (Upper level status lets you book over 3 months in advance.)

I only started using the Marriott program a few months ago, so I don't know if Marriott (with it's 70K + 1 free night cert card promo) has good (in terms of both value and location) in Rome or not.

And I haven't researched Florence, so I don't know what the situation there is.

I do know that Priority Club (Holiday Inn, Intercontinental, etc) has tons of locaitons in Paris, some at good values. And Paris has a better metro system than Rome, which is part of the reason it's easier to find more hotels with good locations (near one metro stop or another) in Paris than in Rome.

However, I do know that if you use your Priority Club points in one of these cities, you're not likely to have enough (from just one card sign-up) for other cities. So unless multiple people in your family are going to apply for the same cards (use one person's account for Rome and another person's account for Paris, for example) you're going to have to mix programs to stretch the points from sign-up bonuses.

Most hotel cards earn points pretty slowly on "everyday" spending. In any reasonably short period of time, you'll have trouble getting a lot more points beyond the signup bonus. So unless the trip is very far off, realistically, you have to look at what you'll get form the sign-up bonuses and not count on much else from actual spend...

... I would recommend the Priority Club Select Visa from Chase as one hotel card you get to take to Europe, as it won't charge you foreign transaction fees, which most other hotels cardss will. (The other hotel cards that don't charge foreign transaction fees include on for Marriott and one for Hyatt. All 3 of these are from Chase.)