I have completely stopped using Storyboards and Xibs in my last few projects, two of which have been quite large. I find the code so much better for it. So I wouldn't be put off Xamarin because of a lack of Interface Builder.

I am also really loving Swift when you can use it on its own (I.e., without relying on an older Obj-C based library). The strictness of the type system eliminates many runtime bugs.