I only deal with A.N.A., P.C.G.S. and N.G.C. in order of preference respectively, certified U.S. mint coins.
A.N.A. is of course, the best grading system to go with, but, using grading systems simply avoids the "counterfeit" issues all together, and insures that the coin you get is of the highest quality grade.
I normally only purchase coins in MS61 or better, as long as the price isn't exorbitantly high, however I will settle for a VF coin, if it is a rare find.
Other than that, unless you are collecting some very old Spanish bullion or more exotic coins, there really isn't much worth collecting except for simple sentimental value.
