<p>which library better for faster java application swt or swing?</p>

According to wikipedia there is no clear winner (although you can edit that if you want). Inevitably, you can write benchmarks which will show either much faster that the other. Swing has more freedom to optimise on the Java side of things. SWT can allow more optimisations to occur within the windowing system.
Probably the bigger impact on performance is going to come from how your application behaves. Concentrate on getting your code clean (and do a little profiling when necessary).