USB OTG (also called USB On-The-Go, or USB Host) is a feature that allows USB devices such as a tablet to act as a host so that you can plug-in other USB devices such as a USB Flash drive, and the tablet can then share data with the USB device. It can be a helpful feature, but not every tablet has this feature.
Which Galaxy Tab 3 Tablet to Get?
The Galaxy Tab 3 8″ and Galaxy Tab 3 10″ have this feature. However, the Galaxy Tab 3 7″, being the most low-end model, doesn’t support this feature (there’re false reports that Tab 3 7″ supports this feature, but it’s already verified by many users that it doesn’t).
If you want a low-cost decent tablet, then the Tab 3 7″ should be good enough. However, if you want this USB Host feature, then Tab 3 8″ would be the better option. If you want a bigger screen (e.g. better for watching movies, reading comic books or editing documents), take the Tab 3 10″.