Peppermill & Atlantis are both good. I look at things a bit differently - where are the best odds for slots; definitely not downtown on Virgina St! (Silver Legacy/Circus/Eldorado/Club Cal Neva/Harrah's). Walking around those spots isn't a good idea either, as this part of Reno seems to attract the crack-heads & derelicts...
HOWEVER, if you are going to stay in-house the three listed by others (Eldorado/Silver/Circus) are good. Another reason to choose them; if you have serious play on an MGM/Mirage One-Club card. BTW: Silver uses shufflers on all BlackJack tables - a BIG NO-NO in my book! Although you can find no-shuffler single deck at Circus, and double deck at Eldorado...

Atlantis & Peppermill are BIG, and offer a good mix of slot odds/shopping/restaurants & other things to do. Sienna is a little calmer (very friendly dealers), has a good restaurant & wine bar, and overlooks the Truckee River.