+1, we use Hellosign's API and love working with the Hellosign team. It was incredibly easy to integrate their API into our workflow. We actually have a case study with them here: http://blog.hellosign.com/esignature-api-powers-bintis-rapid...

One of the best parts of working with Hellosign is their amazing tech support team. They are incredibly responsive (and nice!), and have helped us troubleshoot issues on many occasions. We are on a first name basis with these guys, and would recommend working with them!