Difficult choice! I actually use the 507MKII on my Aries 3 and I LOVE the ARM. The 507 is so stable and so solid that it exudes solidity and confidence. It is a pleasure to handle and use; it's not flimsy or bouncy like so many uni-pivot arms... I really don't think that you can go wrong with the 507 MKII. I believe it has a slightly more 'solid' sound than the Graham with less 'air' overall and that it projects a more centered sound stage. Really, between the 507 and the Graham I believe it would come down to personal taste and system matching. I don't see how you could go wrong with either.
I'm not crazy about the VPI arms...my advice, stick with the Dynavector or the Graham; either will most likely last a lifetime...
I'm not crazy about the VPI arms...my advice, stick with the Dynavector or the Graham; either will most likely last a lifetime...