Which Topbox and why?

[VMAN]

I am looking to buy a topbox for the GS.
BUT, which one and what do you look for?

I have seen people rave about the 650's box, but no-one can tell me why?

 

[Chrisl]

 

[VMAN]

 

[Chrisl]

 

[Mzee]

 

[Postman Pat]