Both characters really develop during the show (which I love… especially because they are both two female characters).
If you love the musical I REALLY recommend the actual book Wicked: The Life and Times of the Wicked Witch of the West by Gregory Maguire. Warning: It's for adults. The musical is VERY loosely based off of it, so it's like having two Wicked stories, which is awesome.
Elphaba will always be my favorite character, but because of Maguire's book. No Good Deed is my jam.
The original cast will NEVER be in the movie. Kristin Chenoweth is going on 46 years old and Idina Menzel is going on 43. So unless they chose Kristin to play Morrible and Idina to play… who knows, they will NOT be in the movie.
I honestly think that they will wait until audiences die down from seeing Wicked on Broadway, which will be a VERY long time yet.
However, if they do decide to go forward and actually start making progress soon (there's been talks of a movie ever since Wicked opened in 2003), then I'm hoping Anna Kendrick or an actual Broadway actor will be playing Elphaba!