It all really varies though. Some schools of thought say start small and build your way up. Certainly that is what I hear they do in Europe and there is definitely merit (and safety) to that. There is no "best bike" because all beginners are not equal. All things considered, starting smaller is always a much safer bet.
Someone once told me to get the biggest bike I thought I could handle because I would outgrow a smaller one quick. The choice really depends on the person, their ability and above all, responsibilty.
I took heed to that and talked to lots of experienced riders before getting one. My Busa is my first and only bike thus far. I have had the great advantage of riding with a number of more experienced riders and have gotten excellent tips and advice.
Keep in mind I could not have ridden one in my 20s (nor afforded one, frankly) and that it is one of few bikes that I could sit comfortably on at my height and weight without feeling like I'm on a Tricycle.
I rode a buddy's ZX10 to his road test and refused to ride it back. Most uncomfortable for me.
I found a sweetheart of a deal on mine and took the leap and havent looked back. I definitely would not advocate the average person starting this big though. Personally if I started on a 600, that bike would not have lasted 2 months.
JMHO . . .