John Deerfield , May 01, 2011; 12:35 p.m.
My vote is for the Op Tech straps, but they do make a dual harness system (http://www.bhphotovideo.com/c/product/643694-REG/OP_TECH_USA_6501032_Dual_Harness_Regular.htm) which is what I use along with a newer dual sling system, but I am not sure what the difference is. The advantages to the dual harness over the Black Rapid dual strap (which I also used, and is available for sale!) is that the cameras are far better balanced, when I left one the other doesn't drag down. I can also use a strap from each side to carry just one camera. And finally, I am not giving up my tripod socket. I tried using two independent camera straps but in my case, they just crisscross inconveniently all the time and I kept fighting the strap(s). One other nice thing about the Op Tech system is that I can put the connectors on each camera and then my wife, who doesn't like dual straps, can just attach it to a single strap: no fuss.
I personally do not trust the Manfrotto tripod plate's ring to hold my camera (when I used the Black Rapid). Over the years, I have had three of those screws simply come out. I don't know they just wiggled out of the washer over time... but for me, it really doesn't matter: I am NOT putting that kind of load on the plate. In which case, yes, it is more than seriously inconvenient!
Finally, I don't think there is going to be a dual strap that will hold a bracket, especially a Stroboframe. I say especially a Stroboframe because their flip brackets tend to "flip" fairly easily. I don't remember them having a locking flash bracket arm. The only one I can think of that has a locking flash bracket arm is the RRS wedding pro. On occasion, I do use that bracket on the dual harness system, but only if I really need too, it is bulky to say the least. That said, in terms of flash brackets, I haven't found anything better than the RRS Wedding Pro.... and we have used a LOT of different brackets over the years.