I'm playing as Sylvan and I've chosen:
Level 1 - Nymphs. I think they are more useful than Dryads. After all, healing Ents is important!
Level 2 - Dancers with the Wind, I think they are better than Dancers with Death. Because a direct, strong attack is better than a medium attack on everyone standing around. Especially for level 2.
Level 3 - Master of the Bow and Sniper, 50% each. There are different opinions here. What is better, one super-strong shot or two strong shots?
Level 4, I haven't figured out yet which is better in the Druids.
Level 5 - Battle Unicorn, I think it's better than Light. It's better to have protection from magic.
Level 6 - Wild Ents are better.
Level 7 - Crystal, I think it's still better! :)