Restrooms are a problematic issue, but the concensus among various crossdresser forums is that women’s rooms are far safer. Better to get slapped than punched out.
For what’s worth, a female friend of mine tell me women are generally so preoccupied with finding a stall, or talking with someone, or checking their make-up that they’re not usually paying much attention to what’s going on around them, so it you’re quick and confident about it, you probably won’t have problems.
Generally, it’s best to go in, do your business–making sure the feet are pointed the right way, wash up (women don’t skip this step) and get out. Don’t adjust your make-up, strike up conversation, etc. And be sure to clean up the seat if you miss–it’s just good manners regardless of how you’re dress.
If someone is confrontational, just let them know you don’t mean to intrude but you really need to pee and it’s not safe for you to use the men’s room. If they’re still confrontational, then discretion is the better part of valor–so just go ahead and leave. It’s not necessarily illegal, but you can get charged with “disturbing the peace” or whatever other charge that might come to mind of a cop–and you’re the one who’ll have to disprove it.
If there’s a single-stall restroom, then using the women’s isn’t really an issue. In the States, there’s an increasing number of “family restrooms” that are also single-stalls (also with baby-changing tables) and single-stall restrooms for the disabled that are the best choice for the crossdressers out on the town.
