Willow started practicing witch craft in the last episode Becoming in season 2. Willow was slowly getting stronger in season 3 but she has definitely became one powerful witch in season 4! Technically she was the strongest in season 6 after Tara died.

I also liked her in season 1, which you never listed.

Sorry I forgot season 1. My bad I thought it was listed! The poll is based on the growth of Willow's powers.

^I'd say it was also based on character development, story lines and Willow-centric episodes, best scenes for Willow, even which seasons included your favourite Willow pairings or pairing moments.

Yes exactly! As for the growth of Willow's powers go season 4 is her best season! She's more powerful in season 6 but you can't really count that because those weren't her powers they were borrowed evil magic! But based on personally Willow's best season is season 3!