What is the best program for drawing webcomics?

So I was given a bamboo tablet for christmas last year and I really like it. About three weeks ago I started a webcomic on a free webcomic hosting site. Although my comics are turning out alright they still don’t look as good as I’d like them too. Im using Paint shop pro 2008 at the moment. The lines I draw are shaky and I can’t do any sort of shading. I know that some people are able to smooth their lines and stuff but I’m not sure how.

I’m just wondering if anyone could recommend a good program for drawing with a tablet?