After years of playing the trombone and having to deal with finding the perfect case for my trombone in what was very much a trial and error fashion (resulting in many crumpled bells and dents), I finally settled, about three years ago, on the Marcus Bonna tenor trombone case.
It exceeded standards of all previous cases that I had used in so many ways. For one thing, it is extremely light (for a trombone case) and has two brilliant shoulder straps which can be very helpful if you are constantly having to carry your trombone around town or on the bus or train. There is a very good sized sheet music compartment on the side of the case as well as the case's best feature, an extra length of case past the bell to accommodate a mute. The days of having to bring an extra bag with a mute in are gone! The case is very strong and protects the trombone which can be securely strapped into the case with velcro straps.
All in all, my trombone has never been dented from being in this case, which given my track record with this sort of thing must make it a very safe and secure case indeed!