What is the best PAC system that is used in the markets nowadays? For training and testing purposes, do you recommend any DICOM server/viewer free SDK?
I will not say it's the best, but the Conquest dicomserver is free, easy to install and configure:
http://ingenium.home.xs4all.nl/dicom.html
As for SDK, I recommend DCMTK:
http://dicom.offis.de/dcmtk.php.en
As for a dicom viewer... the Conquest dicomserver does a text dump of dicom tags. If you want to view an image or a volume, you could use the K-Pacs viewer (it is/can be integrated with Conquest):
Two of the most useful tools that I found when using Windows were ConQuest PACS and Clear Canvas Image Server.
Typically, when I'm developing a very generic feature I'll use ConQuest. It's light-weight, easy to run interactively, and inherently contains useful development tools in the interface. I would recommend this for getting started.
Clear Canvas Image Server is a very full-featured product. I would treat that as an actual PACS. When your testing needs to get more intense, you can lean on Image Server. With this you can test things like concurrency and set up long running processes.
Both Image Server and ConQuest are free and open source products.
When you have to develop extremely specific interfaces, you really want at least a trace of the other systems interaction. Dicom has dialects, you may need to learn a few.
Conquest is @ http://www.xs4all.nl/~ingenium/dicom.html