Well, neither is " casino camping"
They are campgrounds seperate from casinos, and both are across the street from them.
The Avi is out of Laughlin, closer to shopping in big box stores... Target, Kohls, Wally World, etc. The only casino close by is the Avi. There is a really nice golf course there too. KOA is much more expensive than Riverside. It is more open, and accessible from the main street.
Riverside is a nice, safe, large RV Park. If you want a two week spot there for the winter, I would recommend calling now. The 400 level is most desirable, as the wind is blocked a little, and it's quieter due to no big rigs (semis running generators all night ) in the lot behind, or off road racing. You will get noise on the upper level.
Riverside is close to all the casinos, to the outlet mall and resteraunts. It is much less expensive than KOA, never had power or water problems there, and never had to worry about any theft or anything like that.
We have been going to the Riverside for over 20 years. I would highly recommend it over KOA.
Good luck!