I actually prefer to write my own backstory, as I almost always do number crunching and backstory at the same time. I start out working on the numbers and as I'm doing that, that gets me thinking on why these numbers are what they are and then I start on the backstory and depending on where I go there I come back and change the numbers.

I'm not always writing a long backstory, but a few paragraphs I almost always put down. Of course, I've played a lot of freeform PBeM over the years, where backstory is the only thing you have, so that might also influence my way of working.

And I've once done a game where we did the opposite. The players came with a backstory and created a level 1 character out of that (that way I could also all give them a couple of freebies). This was Alternity, where character creation can be a bit tricky (and long). Then the players could upgrade to lvl3 and add advantages and disadvantages to the character, so they also had some input and could steer in a certain way if they wanted. Of course, this was with a group I've been playing with for over 15 years now, so we know each other pretty well.