My friend has the RCBS one and I the Lee.
The only way I see that the RCBS is better is that it's made of metal and is sturdier so when you make a throw with it, you can be a little more consistant as there's less flex in the frame. When I use my Lee, as has already been mentioned I have to make a little more effort to make the same movement each time. Not sure if this is clear to someone that's never used one, but it's really not a big deal once you've got the hang of it. Static is also a concern, but bounce does cure it.
The only way I see that the RCBS is better is that it's made of metal and is sturdier so when you make a throw with it, you can be a little more consistant as there's less flex in the frame. When I use my Lee, as has already been mentioned I have to make a little more effort to make the same movement each time. Not sure if this is clear to someone that's never used one, but it's really not a big deal once you've got the hang of it. Static is also a concern, but bounce does cure it.