Obviously, different situations might require different choices. There are some places where it is illegal to use the restroom not designated for your birth sex. Also, which one you use in a crowded biker bar might be different from the one you would use at the opera.
The best plan, by far, is to find a single occupancy unisex restroom. The next best choice would be a "family" restroom.
If none of these are available, I would say you have to consider your presentation. If you honestly believe you pass as a woman (even an ugly woman), the ladies restroom should be your choice. If you are obviously a "man in a dress", the men's room should be your choice.