The UpStrap is a good one by all accounts (I don't have it myself though).
Currently I'm using Op/Tech straps on my gear. These have a choice of neck straps (usually with a neoprene component which is very comfortable) and a choice of attachment straps (which connect to the camera body) which clip together. I use a "Pro Loop" attachment on the right-hand side of the camera body (this is very flexible and is generally out of the way when shooting) and a "Standard 3/8" attachment on the left side (which carries the EOS body's eyepiece cover).
Yes this requires two sets of attachment straps, but if you have more than one body you can mix-n-match. In fact I also have the Op/Tech attachment straps on the external flash battery pack (CP-E3).
I'm not quite sure how the lens size affects this though (or the Sigma's size as Gary would put it
).