Google Nexus 7. Both are low priced tablets with 7 inch screens (Amazon will be releasing its 8.9 inch tablets later this year). The Google Nexus 7 offers all of the usual Google flavored applications while the Amazon tablets go without them. Amazon sells its tablet users content, apps and cloud based storage.
Looking at the web ad impressions between the Amazon Kindle Fire, the Amazon Kindle Fire HD and the Google Nexus 7, the latter had a commanding 68.5% share compared to the Amazon Kindle Fire HD (3.5%) and the Amazon Kindle Fire (27.9%). The original Kindle Fire might have lit a match under the 7 inch low priced tablet category when it launched last year, but the ASUS built Google Nexus 7 now controls that segment.
source: ChikitaInsights, Mashable via Phandroid
The Amazon Kindle Fire HD is gaining users although the Google Nexus 7 is more popular than the Kindle Fire tablets