A good test would probably have a few of all three in order to differentiate among the teams. People on our team in the event at nats said the words were relatively hard. Personally, I'd hope to get the hard words (if prepared well) because it helps you get ahead of those who haven't prepared as well.
Events: Ecology, Herpetology, Cell Bio, Entomology, Sounds of Music, Circuit Lab, Chem Lab, Disease Detective, Dynamic Planet, Five Star, EggONaut, Enviro Chemistry, Fermi, Quantum Quandaries!
Nationals: Wichita: Ecology-4, Entomology-5, Team-11; DC: Sounds-1, Team-11