Pen & Paper Role Playing Games

[Gail Allen]

For years now I've been part of a weekly role play campaign and I have to say I love it.
Through our time we've gone through quite a few different systems for playing - we started out with FATE and have since gone through I think five or so different systems that have been tweaked to not be too jarring a change from what we already played. Now we play a sort of homebrew system (a system that we have made up ourselves) that incorporates aspects from several of the other systems we've tried.
And I wondered; do any of you have any systems that you prefer playing with - and have you maybe tried mixing them too?
What do you think of homebrew systems for playing? I know some people love them but others really like the structure of systems that have been professionally made and extensively tested. Why do you like one above the other?