Pretty much self explanatory. Just state your favorite and give a reason why, or list them from your favorite to your least favorite. In case you don't know the lightsaber forms, I'll list them below.
Form I: Shii-Cho (Kit Fisto's form) http://starwars.wikia.com/wiki/Form_I:_Shii-Cho
Form II: Makashi (Dooku's form) http://starwars.wikia.com/wiki/Makashi
Form III: Soresu (Obi-Wan's form) http://starwars.wikia.com/wiki/Soresu
Form IV: Ataru (Yoda's form) http://starwars.wikia.com/wiki/Ataru
Form V: Shien/Djem So (Anakin's form) http://starwars.wikia.com/wiki/Form_V:_Shien_/_Djem_So
Form VI: Niman/Jar'Kai (Vrook Lamar/ Serra Keto's form) http://starwars.wikia.com/wiki/Form_VI or http://starwars.wikia.com/wiki/Niman_/_Jar%27Kai
Form VII: Juyo/Vaapad (Mace Windu's form) http://starwars.wikia.com/wiki/Form_VII:_Juyo_/_Vaapad
Double-Bladed lightsaber form
My list from favorite to least favorite is:
1: Niman (Not Jar'Kai cause I don't like it)
2: Makashi
3: Vaapad
4: Soresu
5: Shii-Cho
6: Shien/Djem So
7: Ataru