ASP.NET MVC is an official Microsoft-distributed library. See http://www.asp.net/mvc if you have any doubt of this. As far as Webforms vs. MVC, I think coming from PHP, you'll probably be more comfortable with ASP.NET MVC. If you're interested in learning materials for ASP.NET MVC, I posted a pretty lengthy repsonse here.
To expand on the Webforms vs. MVC thing, it really comes down to a matter of preference. Webforms has a lot of built-in controls and makes your traditional web application similar to a desktop application. It was originally intended as a way for Visual Basic Windows developers to bridge the gap between winforms and the web. That said, Webforms is a very mature product with tons of 3rd party controls and documentation available. You can find out how to do pretty much anything with a few google searches when you use WebForms.
ASP.NET MVC is the newer framework and simply offers an alternative to WebForms. ASP.NET MVC is a "closer to the metal" experience where instead of using custom-built controls to build out your website, you write everything yourself. This will be familiar to you having come from PHP, which is why I recommend it to you. Another thing to note is that ASP.NET MVC was built with unit testing in mind from the start. Unit testing is not impossible in WebForms, but it's much more difficult and time-consuming. So if unit testing is important to you, ASP.NET MVC is probably the better choice.
Microsoft has said about 10,000 times that your choice of technologies really comes down to your own personal preference, and they will continue to support both technologies into the foreseeable future. The important thing to remember is that ASP.NET > WebForms and ASP.NET > MVC. ASP.NET is the overall technology, and you just get two different frameworks that you can use to develop with it.
Also, technically speaking, it's possible to mix both frameworks within the same application, although I've never done that myself. It just feels kinda dirty :)
Since you mentioned Steven Sanderson, you might be interested to know that he and Rob Conery have been developing a series of WebCasts surrounding the new version of ASP.NET MVC coming soon. The webcasts aren't free, but they're pretty cheap, and you can find a preview on TekPub, here:
http://www.tekpub.com/preview/aspmvc
Best Answer
asp.net + commercial reporting tool(for example: telerik) + pure asp.net ajax
reasons:
-because it's intranet application, speed in context of bandwidth and page size it is not issue, and viewstate it's not concern
-for reporting, asp.net it is very good because of using of controls which you can bind to data very fast and easily...if you put on top of that some asp.net commercial reporting tool like telerik, I think you get pretty stable and robust system
-unfortunately, asp.net and jquery don't work well together(asp.net id generation issues) so I will recommend asp.net ajax, it fits nicely in whole asp.net page lifecycle system
cheers