I have tried many others and Ninja Forms is by far the best as it is easy to implement and has all the features (and then some) that we need to create high quality / great looking email forms that also let us track our AdWords conversions!!!
Ninja Forms + GoConvert
Use GoConvert and Ninja Forms to maximize the ROI of your sales and marketing spending. Enrich information in your Ninja Forms account, improve contact and deal information, and start visualizing marketing and sales performance. GoConvert works around the clock to automatically fill in missing data. Your insights get better all the time.