You have got to be kidding. Please tell me you're kidding.
Go here and search under "pick" and "weight" and such. The flatpick list has been operational for just five years, and there may have been a week go by without a debate on that question, but I can't remember when it was. You can find enough opinions on the issue to provide you with several weeks reading.
My own personal preference - having in mind that I only do lead flatpicking alone in the kitchen, and when I play "out" it's rhythm backup (albeit with some fancy bass lines now and then) for singing or fiddles, etc. - at the moment is a Fender California Clear medium. But when I'm tired, but still need to make a lot of noise, I fall back on my prior preference, the Clayton "Gold" .94, with holes drilled for better grip.
Link fixed - JoeClone