Which free blog service should you choose Blogger or Tumblr? It depends on what your goals are. If you're looking forward to profiting from your blog, choose Blogger. If you're looking for ease of use and a more social atmosphere, choose Tumblr. If you're looking forward to blogging for free i.e. for fun, I would choose Tumblr, but if you're looking to profit from a blog, I would recommend a self hosted WordPress website.
Google owns Blogger. Blogger allows you to more easily integrate Google's products into your blog or 'Blogger website'. If you're looking forward to profiting from your blog, then Google allows you to integrate important tools like AdSense, Analytics, Google Calendar Appointment Slot and more. AdSense is an essential part of a blog's profit, and this cannot easily be added into a Tumblr blog unless you know how to code(How to add AdSense to Tumblr). Blogger's templates are comparable to what Tumblr offers.
David Karp owns Tumblr. Tumblr has an artsy feel. There's a stronger social atmosphere to Tumblr, which makes it easier to meet other bloggers or just make friends. Tumblr like Blogger is upgradable to a unique domain name. Tumblr is slightly easier to use then Blogger. A lot of Tumblr bloggers are females. Tumblr is a fun place to blog on, but it doesn't offer any significant tools for track stats, or profiting from providing content to visitors. Tumblr is trendier then Blogger.