The case you buy will obviously depend on the level of protection that you want for your device. You should note that the Nexus 7 Folio case is currently out of stock, while the rest of the cases will ship in one to two business days. Click on the source link for the specific case that you're interested in.
Nexus 5 andNexus 7 cases are 25% off for a limited time at the Google Play Store
source: Nexus 7 (Sleeve|Folio|Case), Nexus 5 (Bumper|QuickCover) via AndroidCentral