Go to your local Best Buy and compare the 3. They all have pros and cons. The Kindle is tied into Amazon and runs a custom version of Android. The Nexus has no SD slot but runs the newest version of Android. The Samsung has an SD slot. They all look nice but when comparing them the colors on the Nexus didn't pop like the others. This may have been just the particular tablet I was looking at.
I ended up going with the Kindle because I use Amazon and I am already tied into it.