Many have questions whether sub domain blogs on blog service providers or blogs hosted on www yourdomain com is better.
As an expert in this first for more than 5 years ill tell you both don't have any difference. whether its *.blogspot.com , *.blogsome.com or *.wordpress.com there are no visible differences. As long as your blog has good back links and the feed URLs are facilitated to ping regularly your blog will be indexed regularly. Use some blog software like feedburner which helps in automated pinging from Google blog search and other blog searches. If you are into Google blog search you can be sure of that you will be included into Google search results too. Search Engines love fresh contents make sure you provide the crawlers as much fresh contents as possible.
I recommend you submit your feed URL to Google Blog ping service http://blogsearch.google.com/ping
I am sure it will help