I typically stay in Missionary whenever possible because I feel I have more control over my frame than in Don Juan, though it does depend on the speed and complexity of the move, if stairs are involved, and how comfortable I am with my spotter. If it's a very fast move with lots of obstacles, and if I'm unsure of my spotter's ability to guide me and catch me if I do trip, then I'll do Don Juan so I have a better chance of navigating myself.
It's a good idea to talk with your spotter and explain to him or her what your preferences are in spotting - where to hold your vest, if you prefer to be pulled or poked for navigation, and how to catch you if you do trip. I usually do a trust fall of sorts with new spotters to show them how much weight they will have to support if I do fall. Most are surprised at how much heavier I am with a rig on, which tells me they probably would not have been prepared to hold that much weight in the event of a fall before my showing them, and I likely would have taken them down with me.