Question: I am quite aware of both java and C# .Net .when i try to create a new windows application which are the factors that decide which technology should be opted?
I know of one thing ,for great and faster UI development Visual studio helps a lot.

Answer: 
There are several factors I would consider...

What are your programmers used to working with already? What third party libraries are you likely to need, what's available on both platforms?

Does platform independence matter to you?

Would LinQ be advantageous?

If you're starting from scratch, costs for the platforms?

Both platforms have strong communities around them...

Hope this helps...
Yeah for a pure cross platform application Java can't be beat, but if you can manage it Silverlight is a subset of WPF and a pretty compelling cross-platform proposition on its own.

Productivity-wise I think WPF has an edge as it has a nice XAML markup language that can be easily created with the built-in designer in VS.NET or integrates nicely with MS' suite of expression products.