In all honesty, Wes, I don't think I could say what is the most popular. There are a lot of Nevada collectors (like me) but on this site alone you will find collectors of...

all divernt chip versions, sub sets etc......
Jetons
Antique
Molds
Bone
Wet
Cuba
Horses
Baseball
Octagons
C&S
Illegals
Indina Casinos,
Roulettes
Animals
Fractionals
Hot stamps

and on and on...the thing I noticed as you start to learn all the different chips out there, you don't pick your collection, it picks you. You will naturally gravitate to what appeals to you.