What Is Your Favourite Coin Series Of All Time?

Not necessarily. There are two reasons why most of the answers given so far have been American coin series.

First, most of the forum membership is American, so you'd expect that to sway the voting. It's only natural to be interested in your own country's coinage, and Americans are no different in this regard.

Second, collecting by "series" seems to me to be far stronger in America than elsewhere; I suppose its because American coins are generally so expensive, very few people can afford to collect "American coins" in general, so they narrow the field down to keep their goals realistic. But in my experience, non-American collectors rarely even think of which "series" they collect, or if they do, the definition of "series" is much broader, like "ancient Roman" or "English hammered" or "Australian predecimal". Most of the collectors I've met here in Australia are generalists. With one or two notable exceptions, the only serious "series" collectors I've encountered have been expatriate Americans.

That's not to say the "American way" is wrong; it's just different.

I don't collect by "series", but one of the most interesting for me at the moment is "Chinese cash". For a "series of all time", it's hard to beat: a history 2000 years long and issued by over a dozen countries.

@ sel_691
Sounds interesting
How many square coins in your collection?

DBM: 76 issued for circulation coins.
I am now starting to look at quasi coins, such as NCLT's German square Notgeld tokens, etc. Not quite so enthusiastic, they cost more, and one of my criteria was to keep the costs to minimal levels, to retain the fun factor.