Perhaps the 1974 aluminum cent http://www.lincolncentresource.com/Rare/1974Aluminumcent.html but Christian is more likely correct, as coin days are numbered.
Of course we also need to understand what the OP means by "most collectible". To my way of seeing it some of the most common stuff is most collectible because it is available and the most collectors can have one.
Using the above, and excluding errors/patterns/bullion/commerative, I personally like: 96 W Dime 99 S Silver Delaware Quarter 72 Eisenhower Type II 70 D Kenedy Half
What makes you say that? The hobby has been around to 200+ years already... What makes you think it won't survive another two centuries? :rollling:
I'd guess the 1964 clad quarter could be the most valuable coin. There are a lot of unique and virtually unique coins that could come to represent the entire era. Of course, predicting the actions of future collectors is exceedingly risky.
The 1964 and 1964-D quarters were silver with quite high populations. Is there a 64 clad quarter that I'm unaware of?