Around here and the high demand for home health, many of my collegues would disagree on the flexibility issue. Demand comes demand...and that will overthrow flexibility quickly.
I do agency for a local hospital exclusively...I can do PRN with them if they wish (but they have to buy my contract) which is another way to go flexible...but since I make more money with agency I stick with them!
I choose the days I will work, I choose the facility, I choose the type of nursing, I choose the shifts and subsequently my wages (if I am short one week I can pull a weekend swing and get more money from my differential than weekdays day shift to make up).
There are risks however...cancled shifts or not needing you and pulling you off 4 hours in (I am guarenteed 4 hours)...or being floated all over the place during your shift. But I find the flexibilty and money outweigh those in my situation

. Also, learning on the fly is stressful at first...but you get use to it.
After 4 months of doing this, I chose to work at one hospital exclusively (lucky for me I can do this), and I have a name for myself there. They know me and I am 'one of the team'...in fact, many still don't know I am agency! I am top agency nurse there now...an only after 4 months! If there is an opening...I am called first

!
I love this option and have been so much happier as a nurse!!!!!