I’ve done a lot of work with QLab and Final Cut. In my experience, there isn’t one particular format that works best – it really has a lot to do with the hardware you’re using to push the video via QLab and the projector/display to which QLab is sending the video. If you’re using a 4K projector the “ultimate” file dimensions are different than a 32″ LCD.
In my experience, when I tech says “anything but”, I fire back with “but why?” or “tell me specifically what will work best for you”. Not because they’re wrong (he might have good reason not to use h264, although I’ve used to great success) but because they owe it to you (and their own professionalism) to have a ready answer. After all – if they event goes off well, you both look good!
Sorry, if that was more rant than answer!