Depends upon the person's age, genetics, where they are in transition, and their state of (un)dress.
I would say overall most FtMs can get to the point where they pass more quickly and easily than most MtFs in most situations. Then again, a 40-year-old, pre-T FtM will probably have a have a harder time passing than a 16-year-old MtF, especially if she's on hormone blockers.
However, with enough time and money MtFs can get to the point where even a lover might not know. FtMs will likely never have that option (without making up stories about medical mishaps or birth defects).