My back-end language experience includes mostly c# and Ruby, but I didn't have any issues getting familiar objective-C, learning new languages is usually fairly enjoyable.
Does anyone have advice for which one to choose based off personal experiences?
Update: I should add that the two biggest deciding points for me are development enjoyment and speed of development.
I am not overly concerned with user base since it is possible that Android could gain a lot of ground in the next couple years.