Generally speaking, the smaller the casino the more valuable the card. However, few cards can be found (harvested) from the small casinos, so they seldom yield many cards.

The locals casino cards are usually more valuable.

So, if you only have the car for a couple of days, I suggest:
...A run up boulder Highway all the way to Railroad Pass.
...A trip to North Las Vegas.
...A ride out to Summerlin.

Also there is a new casino called Speedway up on the way to the NASCAR Speedway.

Good luck (cards and cash) on your trip.