Selecting a WordPress theme is not all about the layout and other design elements. Consider also if the theme can pass the test of being XTHML valid.
To quickly check if each theme you like is XHTML valid, run it against this test by entering your WordPress.com URL onto W3’s validation at http://validator.w3.org.
When I ran my WordPress.com URL using this current theme, the test results came out with 3 validation errors. Yes, I wanted a perfect score, but to me anything less than 10 errors is quite acceptable.
Is your theme XTML valid? If it yields with more than 10 errors even without any post yet, drop it. It’s not worth tweaking.