I focus my collecting on $1 Las Vegas chips.
Highest book value: $1 Four Queens 1st issue Arodie in slightly used condition valued at $350
Most paid: $1 Hacienda 1st issue Small Key in average + condition - paid $225
Favourite: So hard. I can't just pick one, so I won't. It is one of these though, I'm a sucker for scalloped inlays, and 1/4 and 1/8 pie chips, and old chips and... (some cheap, some not)
This last picture is courtesy of Silver State Treasures - I do have one in my collection, but have not indexed it yet so no picture.
And to take it one step further and add in the chip I really want, which would be my most expensive, most valueable and favourite:
(picture again courtesy of Nevada Chip Pictures