Tethering vs Built-in 3G/4G for Tablets?

When you're outside of wifi range, do you prefer to tether your tablet to your smartphone, or do you use a tablet with a built-in cell radio for 3G or 4G networks?

I used to think people liked to tether so that they didn't have to pay for separate data plans for a phone and a tablet. However, some people have shared data plans, so that may change how they use their tablets when they're on the go. People may be more likely to use a tablet with a built-in connectivity so that they don't drain their phone's battery with tethering.

What do you use, and why?