50 is the start for the majority of mine. I always have a very specific goal in mind for my characters from the jump so when I'm rolling something new it's already a fully fleshed out character. I come up with an idea, put together a build, PL the character to 50, outfit it, then run through all of the task forces in order. That way I can get a feel for any powers or synergies I may be unfamiliar with and make tweaks to the build.
There are a few exceptions, like if both sets are ones I've never played or if I'm unsure about the final direction on a build. I don't really play melee characters either so on the rare occasion I do I actually do the work.