I actually like ankle holsters, but I find it's hard to conceal (well at least) anything much bigger than a pocket pistol on your ankle. Unless maybe you start rocking bell bottoms.
I've had good luck with a tuckable IWB. I find at 5:00 it just dissapears into my "shirt billow" or whatever you'd call it even with a reasonably fitted shirt. Also, people generally try to keep their eyes of their co-workers butts, so you get a bonus level of concealment.
si vis pacem para bellum