The Diana slide breech rifles have a tapered breech makes for easier pellet loading.
I don't know why the other manufacturers haven't adopted this design.
The AA Prosport is unique in that it has a cut out at the bottom of the cylinder and a hidden interceptor anti bear trap device.
I still like the Theoben enclosed slide breech, swing out single shot tray with a loading probe seating the pellet within the breech.
The BSA rotating breech RB2 was a very good mass production idea as an alternative to slide breech, albeit the transfer port being quite long as a result.