Suggest Vulnerable Box OS.

guys, Which Operating System you want to Pentest ??

Windows! Need to practice Windows skills before OSCP so something similar to OSCP windows box maybe?

Yes. Agree! Hate Windows-boxes! Need more of those :-) ( I don't hate Windows in general, but hate them because I feel lost every time I try hacking one) So absolutely need skills...

Windows with IIS and ASP.NET vulnerable web application.
It's almost always PHP and Apache on Vulnerable boxes, but IRL I think ASP.NET and IIS is more common.