I've got both - my lovely Red Onion SBS and a black NVT Ledbury. Like Smally says, they're pretty much the same although the shape looks a teeny bit different because of the construction method (the sides are pulled out a bit further on the SBS where the loop for the strap is attached, but fold right in on the Ledbury).
The main difference is in the length of the handles - the Ledbury's are longer than the SBS's. Neither goes over the shoulder and both go over the arm (SBS is a bit tight and doesn't hang so well).
I've got a strap attached to my Ledbury too, but haven't really found a satisfactory way of attaching it yet - the straps sort of interfere with the top flap when it's closed, pulling it out of shape at the edges.
Couldn't say that I prefer one over the other, but if I could find the perfect way of attaching a strap to a Ledbury, that's the way I would go for my next one purely because Ledburys are cheaper!