I am also a travel nurse and have been struggling with the same question. I work for two agencies, Aureus Medical and Resolve Staffing which are basically the same. They pay about the same, have approx the same benefits. They try to push me to go to where they want me to go, without regard to my wants.

Bad company (or recruiter).
I've applied with INS because the recruiter is nice
and not pushy. She started off with where do you want to go, what's important to you, and told if she thought I had a doubt about an assignment she wouldn't consider it. Doesn't work on commission like some do. So far I'm impressed.
Are you planning on going on in school? Just a thought, but I was reading yesterday and found that AMN Healthcare is a partner with Drexel University, who offers discounts to those employees. Also they staff at the big hospitals: Mass General, Johns Hopkins, Stanford, Vanderbilt... Drexel has an online NP program I am looking into.
Find a company the pays well, recruiters are easy to talk to, care what you want, ask about completion bonuses, and which hospitals they staff , in case you had one in mind. I've found that many companies are connected to a corporation, so you could be working for someone like AMN Healthcare, even though you filled out papers and spoke to Nurses Rx or RN Demand. (Soliant is connected to Sunbelt Staffing corp, so offers many of the same assignments).
Mostly I've been offered assignments at small to medium-sized hospitals through the companies I work for. That's usually where the greatest needs are. Met some really nice people in Po-dunk, America.
Well that's the extent of my experience. A friend of mine works for AMN and loves them. Another feels the same about Aureus. It can vary person to person. Hope I've been a help. Good luck in your travels.
millkay