I'd say that your choice come down to the 1st generation Fire (cheap), the Nexus 7, the Galaxy Tab 2 7" and the Kindle Fire HD.
The classic Fire is cheap and has a great screen but has Amazon's sucky interface and lack of Play Store support.
The Nexus has good hardware and software as Google intended it, but some people say they have screen issues with them.
The Galaxy Tab 2 7" has similar specs to the Fire, but it has a camera, a microSD slot and it doesn't use Amazon's dumbass launcher.
The Fire HD still has Amazon's shitty default launcher, costs $15 to eliminate some ads and still doesn't support the Play Store, but it has a great screen that's 1280x800 instead of 1024x600.