They are pretty equal when it comes to their skill sets. That's what makes the combination so lethal and that's why most of us were so excited when we heard that Jack signed last summer.
I'd go with the hot hand (until otherwise proven). Right now that's Jack. If Jack's form falls down a notch or two, Jose will gladly step in.
To me, it's less about who starts, and more about actual minutes. I think they will end up splitting their time pretty evenly.