It's easily started, if you think about it. For example, the pennies of 1918 and 1919 have three (quite significant IMO) varieties with the Heaton (H), Kings Norton (KN) or no mint marks. So, do you just want any one, or one of each? I'm a one of each person myself.
Then you get things like the 1902 low and high tide pennies. Ok, I'd best have one each of those too please.
Gradually the differences get smaller and smaller down the line until people start calling flaws, clogged dies and suchlike varieties (I'm not saying that's wrong, but where I draw the line I think.)
So, how about you? One of each or any old one?