If you are traveling on something of a budget but want to build up points and get free breakfasts (as a Gold member), then Hilton can be very good in the USA because it has so many properties in so many locations. But as far as I know, some of the less expensive chains within the Hilton family (e.g., Hampton Inn, Doubletree) offer good value in some respects but don't have lounges and/or their limited range of rooms means that upgrades don't mean much. I hope others will correct me if I am wrong on this.

As suggested by bdemaria's post, I'd suggest avoiding Expedia and other third party booking agents unless you can get a much better deal than by booking directly through Hilton. In addition to the other problems, they can be a real hassle to deal with if you have to change or cancel plans.

If point accrual is a priority for you, by the way, you might want to look into getting a Hilton American Express Surpass Card (if it's available in Denmark or if you'll be in the USA long enough to apply for it here), which provides bonus points for signing up and extra points when you use it to pay for Hiltons and some other types of purchases (groceries, gasoline, drugstores, etc.).