Best 3G/4G tablet?

Im planning to buy a tablet with 3g/4g, I am a college student and i currently own a nexus 7. I really like the 7" form factor but I have absolutely no problem going for 10.1". But here's the catch, I live in Costa Rica, so I need to buy the device unlocked, and to be compatible with the frequencies of the local carriers (they have the same as at&t and tmobile). As we dont have 4g in Costa Rica it is not necesary. I have seen the new tablet z from sony, but the only way to get it is the japanese model from ebay. Also if the price gets above 650-700$, is it really worth buying a tablet instead of a laptop?