As per Forrester Wave 2017 Q1[1] report best RPA vendors are
- Automation Anywhere
- UiPath
- NICE
- BluePrism
- EdgeVerve
- Workfusion
- Pega / OpenSpan
UiPath scores best in the technology category, AA has the biggest market presence and breadth of use-cases while BP scores best when it comes to bot governance and deployment features though, I think, they are a bit underrated.
Secondly it depends on the use case and who you are. For example WF is great when it comes to digitization(OCR) processes while UiPath offers a free community edition.
Similar answers were given by Everest or Gartner.
http://reprints.forrester.com/#/assets/2/661/‘RES131182’/reports