If you're talking about the Tab 2 7.0, then the Nexus is a better device.
Problem with the Tab 2 (I have one) is that its slow and the overlay which Samsung have put on it is unnecessarily fiddly. For example, there's a 'take screen shot' icon right next to the menu button, which is pretty stupid. The buttons are also in the wrong position (left of screen, rather than center of screen), they're not physical buttons, can disappear when you don't expect them to etc. I think that my Phone (S2) blows it out of the water for usability, functionality, and speed.
Personally, I wouldn't get either of them. I'd get the iPad Mini. It's just exceptionally good, better than the Nexus 7, amazingly thin, very light, has an excellent screen, and is also more kid friendly.