longroad is right. Additionally you need a theme that compliments your topic and sets the right mood.
Some themes are better for SEO and some are better layouts if you want certain types or sizes of ads. So there are variables to look at.
All these are pretty good I think.
83 Beautiful Wordpress Themes You (Probably) Haven’t Seen | Smashing Magazine
I've always loved "I Feel Dirty" #21 on the list above.
I feel dirty 1.0 | Theme Viewer
Click test run to see it full screen and live.
I just like it even though a lot of topics it just would not work for.