I feel you'd be best off going ICU first for a couple of reasons. You are automatically drawn to L&D as mentioned in the last post, but it's important to keep your eyes on the prize...which in your case is Nurse Practitioner.
Both areas will provide you with experience that you need, but that coming from the ICU will be more comprehensive. It will be important for you to know how things work in that setting, where some of your patients can and at some point will wind up, etc.
If the 18 month contract seems daunting to you, take a travel assignment elsewhere to where conditions are better for you. You may want to consider travelling to California as the nursing shortage there provides for ample opportunities to negotiate a contract on your terms. Your best bet is signing on with an agency that caters to travlers, and have them hash out your terms (like say, a 6 month contract, housing, etc.) You're likely to find something ideal for your situation, and find that the rate of pay in Cali is good enough to make it worth being away from home for 6 months.
The experience alone should be worth it, but in the end if I where you and considering your path...I'd make sure I hit up as many departments as possible. Don't just think L&D or ICU, consider also working in the OR, ER, etc. for awhile. Getting a feel for how the different areas function and how things work will make you a better nurse practitioner. In fact, this is advice I'd give to any nurse whose job is interdepedant/inter-related to other departments. Planning on working in the ER myself, I'm going to want to know how things function on the floor. At least then when i'm complaining about a slow transfer from my ER bed to the ICU I'll have a feel for what to expect from them
Whatever you chose, good luck and enjoy yourself.