Do you own the complete rights to characters you create or are they shared with the publishers?
The long answer is...
I actually enjoy writing my own characters AND writing for hire for characters other people own the rights too.
The benefits for owning my own characters are that if the miracle of getting it optioned for a film or video game or t-shirt logo or _______________ (fill in the blank with miraculous shot in a million happening) occurs, I can make the cash without having to have my share split or filtered through some company who jointly or wholly owns my work. But the main benefit of owning the copyrights of my characters is that I have editorial control and artistic control over the vision and "purity" of the work. To put it in a more current understanding, you won't see a "Before Rick Ruby" or "Before Fishnet Angel" comic book series made without mine and Bobby's blessing and legal approval. (But we're open to it. Please send large checks to me and Bobby at our currently addresses. Well, what are you waiting for? I don't see any big checks in my mailbox yet.)
The benefits of writing doing work for hire with characters I can't own (even if I create them) is that I get paid up front, and I get paid better because one of the things the publisher is buy from me is the rights to all the stuff in my brain as it relates to their characters and stories. Another benefit, and this may seem to fly in the face of what I just wrote in the previous paragraph, is that I get editorial guidance for the work. I don't have to sweat the small stuff or the plots and limitations because I have someone else to stress out about those on my behalf. But if and when a Gene Simmons Dominatrix movie is made, Mr. Simmons wouldn't owe me a dime, even if it is based completely on the scripts I wrote for him and IDW. I gave that right away and I did so willingly. I would hope, however, that somewhere in the credits I'd get a mention that said "Based on a story by Sean Taylor" though.
This question comes from the wonderful "Table Talk" column at the New Pulp website, which you should all be reading.