Generally, most flatpickers like a thicker rather than thin (or flimsy) pick, with Clayton Golds (.85 to 1 being the average thickness) being the choice of many. One exception is Steve Kaufman, who prefers a very thin pick. Much depends on what sound you are trying to achieve and whether you are playing lead or straight rhythm or rhythm and throwing in licks. For rhythm, I like Clayton Gold .80 or .72. For lead, I will use a Martin .96 or even a Clayton Gold 1.20. I use the aforementioned when I'm jamming at festivals or fiddler's conventions and usually outside.
My favorte pick is a 1.05 tortoise shell pick, which gives me just the "pop" that I want when I hit the strings. They are, however, spendy ($35) and difficult to come by because they are illegal to sell (not illegal to own).
It all boils down to, with what mm of pick you are comfort able and the sound you want to achieve. My suggestion would be to experiment with different thicknesses. Except for the tortoise, the other picks mentioned are cheap and it won't break you to buy several different kinds and thicknesses for experimentation.
I hope this helps and doesn't totally confuse you.