I think depending on the exact nature of how the wiring must be run, both have their strongpoints.
For me, the OptoBranch 4 works best. It's in the rack, its hard to lose a rack(not that I've ever tried), and since I am a one-man production, it's ideal. I can sen 2 runs to the back(or up, or back and up) to two spot towers/positions, while still sending a run to the stage and then having an open send if I should ever need it. But, once on stage, the DMX Branch/4 would be a better fit for me because A: I don't have rack space for another OptoBranch 4 and B: The rugged box can be placed somewhere out of the way and then I can have a split to the front truss, rear truss and the footlights, and still leaving me a send open should I need it. Or, if I'm running MyDMX stageside like I did on my SacAnime event, I could have been up and running a bit faster with a bit less cabling using a DMX Branch/4. I don't like taking racks apart if I don't have to. Sure, I could save money, but for the price and if business takes off, the DMX Branch/4 would be an ideal add-on that I've been considering for quite some time.
In this case, it's not a matter of "right tool for the job" but more of a "which correct tool best fits in with your situation". It's nice to have choices like that.