Who would win? A WFM or a NM?

WFM = 2100 FIDE

NM = ~~2200 FIDE

Really? You must be pretty damn good then 

NM obviously (in general). My best win is an NM

NM is not a FIDE title.  For example, NM in the US is 2200+ USCF (which is usually about 100 points higher than FIDE).  So a new NM and a new WFM would be roughly equal with regard to rating.  However, USCF does not give any higher titles, so they could be 2200 or 2900 USCF and still be a NM.  This means it is possible to be significantly stronger as a NM, while someone with a much higher FIDE rating would earn a higher title so you won't see 2500 WFMs, for example.

Interesting, Thanks!

Never knew that to be honest I am from Athens never been to USA before.

There are not many countries that have the NM title.  FIDE has the CM title for those places that do not give out NM, and there is a corresponding WCM title with lower rating requirements.

Probably the player with the higher rating.

Sometimes, the WFM would win. Other times, the NM would win.

The difference between a 2100 and 2200 is bigger than the difference between, say a 1600 and 1700

Wait.... I thought that USCF has Senior Master for people above 2400.  Has that gone away?

Kind of.  It is a separate designation, but not a separate title.  They also have "Original Life Master" if you maintain 200 for over 300 games.

Correction:

WFM is 2100 FIDE.

NM is 2200 USCF.

2100 FIDE is approximately equal to 2200 USCF (give or take).

So an NM vs. a WFM should be a relatively equal match.

Though of course, what should happen isn't always the case ...

WFM is sometimes given out for tournaments or special things like that so it’s not always 2100 fide but usually is, depends on who the NM is and who the WFM is