If you've never ridden anything before, here's my opinion:
-start on a 500 or less (ninja 500/ suzuki gs500 are great starter bikes).
-buy it old enough so that it won't depreciate in the year or two it takes you to learn and become comfortable. When (not if) you drop it, you won't care.
-upgrade to a 600 after that.
I rode dirtbikes all my life then bought a 1995 Honda CBR600F3 when I turned 16. It was an awesome bike but I was pretty tiny back that and I did drop it once or twice, and was rear-ended once - took some getting used to the extra weight from dirtbikes, but not so bad.
I then sold that bike and bought a 2003 Honda CBR600RR - that thing was awesome!