I'm using the Crumpler Industry Disgrace
Haven't used the OPtech but online reviews seem favourable.
I personally use the brown crumpler/ orange icon strap.
Looks-wise: very happy with it. (the flourescent icon really stands out.) If you manage to get the ltd ed camo one, lagi outstanding...
Functionality: no real complaints, a little chunky when trying to shove everything into my kata3n1-20 (maybe my bag too small... )
Strap is long so I sling it low across my body so I can do "almost' like a "R-strap" draw, comfy over long periods, kinda balances with my kata sling on the other shoulder when I do that. Never hung it over my neck cos makes me sweat... When slung on one shoulder at the side (like a ladies handbag), rubberised texture of the wording underneath the strap does keep it from sliding clean off your shoulder but then again I'm always semi- 'jaga-ing' it when i sling it like that so be warned .
If anything else, the crumpler is definitely more comfortable than the standard canon strap they throw in with the camera.
My 2 cents.
Canon EOS 5D, 24-70 f/4 L IS, 50 f/1.2 L, 70-300 f/4-5.6 L IS, 600EX-RT. Sigma 12-24 f/4.5-5.6 EX.
Using Kata strap... removable neck strap, and the camera can clip onto my Kata backpack shoulder straps.