I used wufoo in the past and i recomend to use formtitan or formstack.
Both tools have optimization features which are lack with wufoo and jotform.
By far formtian is a winner here, not only it is full of elements, features, no layout restrictions, it is also has a built in conversion rate optimization system.
Thank you for your kind words!
Building a form builder is not so easy, but what make us different is the conversion rate optimization engine, its really going to help you.