This is just my opinion, and I'm no specialist, but I do have some grapes. I'd let them go until winter.
I don't think it's a good time to prune them when they're actively growing. Yours don't look that big. What kind of grapes are they, because some are more vigurous than others.

On the other hand, I don't know what to do with mine. They're totally taking over, growing like crazy. Already grew like 5 ft. just this spring. I pruned the heck out of them in the winter and they responded in the spring with a ton of growth and they're heavily loaded with fruit. The really vigurous one is a "Seedless Thompson". It's also having some mildew problems at the moment. I had to seriously cut back on water.

You could prune them, the cut site will drip sap for a while, but it won't kill them.
But what I would do is choose the branch that you want to train up and get it started on a stake. Then for the others, just do a pinch at the tip. That will make them branch out a little and also send a little more energy to the main branch you are training up. Then next winter, after they are dormant, go ahead and prune out all the side branches.