When anyone decides to start a blog, the first and foremost decision one has to take is to choose between WordPress and Blogger.
Here is what Matt Cutts has to say.
In such a situation the main site on the root domain and the blog in the sub folder both get adversely affected and lose the search presence. But, if you have the blog on a sub domain which is not hosted on your server as in case of Blogger then both the entities remain separate and even if the blog gets hacked then atleast the main site continues to do well on the search engines.
March 6, 2013