If I were asked to choose only three differences--and they had to reflect the daily experience of men and women--then I'd go with the following with one caveat: that I couldn't keep it to just three. Four was the best I could do.
1. Concern about Sexual Assault: When a man walks down an empty hallway or up a quiet street, he seldom needs to worry about being raped. How often does a woman do the same without concern about rape somewhere in the not-so-deep recesses of her mind?
My wife puts it another way: If a naked man were to walk into a room full of women, the chances are he won't need to worry about being sexually assaulted. If a naked woman were to walk into a room full of men, she would be very lucky if she weren't sexually assaulted.
2. Being Able To Pee Standing Up: If I as a guy had to sit down every time I peed, I'd seriously consider shooting myself. If a woman were to inhabit a man's body for a week, I do believe this would be the thing she missed the most.
3. Concern about Pregnancy and Motherhood: It's not like we guys aren't on the hook financially for the children we spawn, but women are way more stuck in the child-rearing arena than men often are. Double that for being able to enjoy sex without concern about unwanted pregnancy.