I own and use mostly RCBS dies and use their competition dies. I like these dies for two reasons. First, you can drop your bullet into the sleeve through a window and it'll like the bullet up. I tend to spin my casing 3x and seat in increments to ( as claimed ) reduce runout. Secondly, I've read articles like on Midway.com that says you can interchange the parts. So, you can covert your 7RemMag for example to a .308 by buying a few parts. I don't know how difficult this is because I have more than one competition die already. I haven't broken out the Forster Competition die sets out because I'm not far enough along on my test loads. This is a top end die that I read the US Army Sniper School uses. So, I figure, if it's good enough for them, it's good enough for me. This is not to say the RCBS dies is a slouch. In the book, Long-Range Precision Rifle by Anthony Cirincione depicts an RCBS Competition Die. I haven't used my Lee Dies too for the same reason as the Forster Dies. But, I did have a custom collet die made for my 7.7 Arisaka and it works fine. I have yet to compare loads resized with this die and my RCBS set.
and have purchased Lee and Forster dies to compare to them.