Hi Kim...I knew someone was going to give you a "flip" answer... Ignore them!

I don't think there is a hard-edge rule or definitive "difference" that clearly identifies one side as "front" or "back".

I checked the glossary before I posted, but there aren't any "rules" there either (because there aren't any... that might be an offer a determination.

Archie pretty much covered it...
I also consider the side with the more "promotional" artwork the obverse (the event, person, place or thing the chip is featuring)...
and the side that promotes "more of the casino" (less than the other side I guess) the reverse - especially if the "casino" side is standard or repeated on other chips.

Sometimes, it's just hard to tell. The HAN's (Hot August nights) are like that. Both sides can have unique and interesting artwork.
In those cases, like Larry said, "pick your favorite side".
I personally take a different approach... I pick the "biggest" car