I haven't tried the charlie banana, we didn't get on with the fuzzi bunz so I didn't bother. The fit of the Smartipants strikes me as inoffensive, i.e. can't see if not being a good fit unless it's on a very chubby baby with very skinny legs or visa versa.
The Smartipants are a great alternative and cheaper too. They are cut a little more generously which is great for bigger babies, and the MF insert is SO SO SO thirsty! We really love them in the office for both little boys!
They are definitely worth a shot, especially as they are on 3 for 2 at the moment, so they work out even cheaper