I have only been using SyncFusion's Essential Studio for the last two months, but they are the best component supplier I've ever worked with. Their source code is well documented, their class and component documentation is detailed and easy to use and their product works very well. With regards to support, it'd be tough to match their quality seeing as I get a response within 24 hours with not only a description of where I went wrong with something, but also a fully-working Visual Studio solution demonstrating how to do whatever I asked.