I've been using the SyncFusion...

jasoncOH, USA4 star
I've been using the SyncFusion WinRT suite on a new greenfield Windows 8 RT project. I tried it and the Telerik suite and I like the SyncFusion one best. It has more controls and seems more complete than the competition. When combined with their free Metro Studio app, you get a really nice set of icons and controls to build slick looking WinRT applications. The controls are easy to use, very intuitive to work with and I've found their support responsive and very helpful. In my case, I was trying to do something and couldn't get it working. Within 24 hrs of submitting a ticket to support, I had a response with a sample app demonstrating how to do what I needed to do. But that leads into why I give the suite 4 stars. I should have been able to find guidance on what I was trying to do but the documentation is thin. However I've found that true of any new component suite from pretty much anyone so I can't hack on Syncfusion too much for this. However, if you have experience with these component suites on any other xaml platform you should be flying in no time.