I am not too familiar with the PHP CMSs, but I can speak to Sitefinity CMS.
Sitefinity is a very developer friendly CMS platform. It is a CMS for ASP.NET that doesn't "reivent the wheel" or significantly change the way ASP.NET works. If you're an ASP.NET developer (or have any ASP.NET experience), Sitefinity will be very familiar. For instance:
- Themes = MasterPages
- Modules = UserControls
- Config = Web.Config
For developers, it's also like "one big API." The APIs enable you to do everything from create pages to edit content to modify and extend the Sitefinity admin. In fact, there was a webinar today talking about the APIs. You can probably find the link to the recorded version later here, though:
Sitefinity API Tips & Tricks Webinar
Finally, for your end users / clients, the Sitefinity tools are very friendly. Sitefintiy ships with the Telerik RadControls for ASP.NET AJAX (leading UI components for the web), so you get great tools to work with that your users can easily use.
Oh- and Sitefinity is very affordable compared to most other commercial .NET CMSs. It's usually $1000's of dollars less than some of the other Enterprise-grade CMSs it competes with.
Hope that helps. More details and demos (of course) are available on Sitefinity.com.