First, the tab 4 has a quad core processor vs. dual core processor on tab 3. The screen resolution is the same at least between 8 inch models. Tab 3 had Android Jellybean vs. tab 4 has KitKat. The shape and size between 8 inch is very similar and I was able to use a tab 3 8 inch case for my tab 4 8 inch. Not a perfect fit, but close enough for me that I don't feel I need to buy an extra case.

The processor really makes a difference in loading websites and opening apps. Also tab 4 allows for multiple user accounts on one tablet and also features a kid friendly account that parents can control access to.

In terms of weight, size, and physical characteristics, there is little difference. However, instead of the glossy back on the tab 3, the tab 4 features a textured plastic back and can make it feel cheaper than the previous models. The textured back is supposed to make it easier to hold, but if you have it in a case, it kind of seems unnecessary and makes it feel cheap.

Hope that helps you make a decision. Price point is probably the biggest difference. IF price is not a concern, go with tab 4. If it is, then go with tab 3. The differences are not so great that it will make watching movies and reading email a big deal.