I have been experimenting with different bloging platforms in the last week. I've come back to blogger where I started my blog. I can't find a blog site that does exactly what I want, yet.
I played around with wordpress.com. It's got a lot of great tools, lots of plugins, widgets etc. I liked wordpress.com but for flexibility of layout I was more comfortable with blogger.
All the blog sites give you access to flickr that works very well. Only Vox did not display my twitter stream very well. Wordpress.com and blogger really make twitter a part of your blog.
Wordpress, Vox and blogger all seem to have good commenting features.
More experienced bloggers may have better better reasons than I do for choosing their blog platform. But I find it easy to write, design, layout on blogger for now.