When choosing among best WordPress themes for social media blog, or any other purpose there are a few rules that one should follow. These rules are applicable to almost all cases.
- What things you want to do on your blog.
- What kind of content you will be posting
- How lengthy your average posts would be
- How many images you will be uploading do you need gallery and jquery effects for your galleries.
- How you would like to showcase content on your main page.
I myself use a simple pencil and paper approach to create initial sketches of my websites before going out and looking for themes.
There are several hundred free themes available in the official wordpress repository. Some of them will fit all the requirements you have for your website in your mind. After finding those few, you need to eliminate the ones you don't like. In the end you will have no theme or just the one theme that will probably need a lot of configuration to be exactly like what you want it to be.
There is no theme that will fit all your needs, no such theme has been created by anyone yet. So you need to find a theme that provides the basic functionality you desire and then start modifying and configuring it to meet your needs.
Now since you asked for Themes Specifically, these are the themes that I like the most and I think these themes are flexible enough to easily modify for many different kind of websites:
- Twenty Ten – The most downloaded WordPress theme of All times, also look around for TwentyTen child themes. This theme is probably the most powerful Free WordPress theme ever.
- Thematic – A theme framework with many child themes available. Thematic is very powerful and can be fully customized via child theme.
- Arras Theme – It is a nice magazine style WordPress theme with sliders featured posts and a lot of features. I don't know why it isn't in official theme repository.
- Minimatica – A nice minimalistic style wordpress theme with a lot of options. supports featured images, custom header, custom menus, etc.
- Grisaille – A simple nice wordpress theme with an elegant emphasize on visual appeal and typography. Supports featured-images, custom headers, menus, social media icons on top, etc.
For a more wide variety of themes you would probably want to consider some premium themes. ThemeForest has some good collection of premium themes for different kind of websites. There are also a lot of blogs that publish lists of premium themes (with affiliate links) for different kind of websites.