iPad mini: Lightning connector
Google Nexus 7: Micro-USB
Amazon Kindle Fire HD: Micro-HDMI, Micro-USB 2.0
One drawback of the iPad mini's ultra-slim build is that it's too thin to include either an HDMI or USB port. Instead, the new tablet comes with the Lightning connector that Apple debuted with the iPhone 5. Because it's smaller, the Lightning connector requires the purchase of an adapter to synch with most iPad and iPhone accessories on the market today, but, according to Apple, it also significantly boosts data transfer rates.
The Amazon Kindle Fire takes home the gold in this category, delivering both a micro-USB and micro-HDMI port for video output to HD TVs. The Google Nexus includes a micro-USB port, but no HDMI.