I looked at Gravity Forms, Contact Form 7 and Formidable before settling on Formidable Pro. Aside from having a lot of features I was looking for and being pretty easy to deal with, the two things that won Formidable for me in the end was having a free version that I could try and the tremendous support that Steph provided @ strategy11.com forums before I was even a customer.
Alex Kelly (Dublin Robotics)
I'm really liking the new Formidable plugin. All the functionality of Contact Form 7 with a much better UI .... I feel like I've finally found a form-maker plugin I can safely hand off to clients!