What Country Do You Find The Most Difficult To I.d. Stamps?

Another vote for the watermarks of Brazil.

Simply awful.

U.S. Postal stationery with the different dies & Papers.

I agree with Greek hermes heads, along with early Austria, where the printing and impression determines identification, so the inking and state of the plate can wreak havoc with the ID.

Outside of that my difficulties lie less with specific countries, but in general:

1. Telling legitimate from forgery or reprint (Persia, German States, Italian States, etc.). In many cases Scott is woefully inadequate. Footnotes that state "Reprints exist" or "Forgeries exist" without diagnostic pointers are less than useless.

2. Telling legitimate postal cancel from fake. Italy, German area, etc. In many cases used stamps are worth far more than unused, so outside of finding the stamps on cover or piece (and even then its iffy), it's a minefield.

Oh, I forgot... one area that rolls all these fun aspects into one and will make your head explode, should you decide to venture into it: U.S. locals. I have the 3-volume Larry Lyons encyclopedia on locals... HOLY CRAP! I could go insane trying to navigate those waters.