Comparison between SharePoint workflows and third party workflows

In one of our client discussion, looking for capabilities and feature comparison document between SharePoint 2010 workflows and other available third party workflow tools (like Nintex, K2 etc..)
So that based upon on our explanation, he was supposed to tell the requirement I hope.
After googling, I got the below info which was worthy to say about
• 1)K2 appears to have the most mature products. Both are quite pricy, though they are supposedly reworking their cost model. Their blackpearl product is a trimmed down version that focuses on SharePoint integration, so hooking into other LOB systems will be limited, but still possible. Allowing the workflow engine to be separated from the wss front end server, not so in Nintex.
• 2)Nintex appears to be a step up from SPD 2007 and 2010. Compared to K2 blackpoint (their SharePoint/Nintex competitor price wise) Nintex has some Active Directory and Exchange actions that could come in handy for provisioning new staff.
• 3)K2 has an upgrade path to their blackpearl full product, which provides an environment/api for creating custom enterprise data connectors so your workflows can integrate with any system. Nintex has an api for developing custom actions, though not as completely defined.
4)K2 has AD and Exchange integration today (for read and email purposes ) but just announced rich extended AD and Exchange integration (see http://www.k2.com/en/blackpearl.aspx - Look in "whats coming" TAB) in addition to lots of other capabilities.
5)K2 provides a range of visual designers (from one built on Silverlight 4 and embedded into SharePoint to a standalone designer and one fully integrated with Visual Studio (2008 and 2010), a very rich "sharepoint integrated " process management capability called Process Portals and rich out of box reports and analytics.
6)K2 also has amazing Infopath Integration and fully manages Forms and Process versioning and lifecycles , something critical to any process requiring Infopath.
7)K2 also adds some really important workflow fundamentals out of the box. SharePoint Designer is a cool tool, but you will very quickly run out of steam, especially when you have to think about issues like how to "go back to a previous step (one or more steps back) in the process (eg a re-work capability)" and do this at multiple places in the process. Many real-life human workflow processes require this ability . Just three other examples are support for time zones, working hours and rich rules capabilities that are highly extensible through K2 Inline Functions.Hope this helps out you as well.