After having it for a few weeks, SWIMBO and I can not report anything negative about our TEK/Sony AWG2021. Well, we couldnt open its case - but it has worked reliable for a few hours since we bought it for like 200 USD (was a real steal).
Its user interface makes creating waveforms easy, and it has GPIB and even an FDD for loading data quickly. IMHO, the user interface is really important with an AWG: if you find yourself planning to enter the functions value by value, you will chuck the unit against a wall soon rather than later.
Re THD: sorry, no idea re that.