The KFHD on sale today is the updated model that launched a couple months ago. It's running the new FireOS 3.0 Mojito on a dual-core 1.5GHz CPU with 16GB of storage. This tablet is missing the camera and HDMI port found on last year's model, but it is also (for the time being) $80 cheaper than the retail price for last year's KFHD.
The Kindle Fire HDX is running Amazon's own Mojito OS on a 2.2GHz quad-core Qualcomm processor with 2GB of RAM, Wifi, Bluetooth, and a camera (more details here). It has one of the best 7" screens on the market (1920 x 1200 resolution), and it even tested better than the screen on the new iPad Mini in a recent test.
It comes with either 16GB, 32GB, or 64GB of Flash storage, and since this is a Kindle you can get it with or without ads. Only the Wifi model is on sale today, and only while supplies last.