Which type of locker shelf would you recommend?

I've tried the magnetic one and last year that broke for my friend that I'm sharing my locker with, but I still have mine and it is in very good shape. There is a small metal one i've used before that has crosshatches of i guess you would call them metal wires and that was too small. There is also the adjustable one that I haven't tried yet, but I have. I heard that the adjustable one doesn't hold well though and I am sharing a locker so one of us would use the top shelf and need to put heavy books on it. Which would you recommend or are there any other ones you could get at office depot?