Saying this is better or that alone will not suffice, when we pitch for some platform, we should justify it too.
Here we are not talking about just 2 but 3 platforms actually.
1. Blogger (Blogspot)
2. Wordpress.com
3. Wordpress.org
Blogger is good for beginers because it is easy and takes care of most things. Also, there is absolutely no cost involved. However, the level of customization you can achieve in Blogger is limited and so is the flexibility of the template.
Wordpress.com is the same as Blogger, however the flexibility is much lesser and they dont allow adsense.
Wordpress.org has evolved from a Blogging tool to a Content Management System. It gives a lot of flexibility interms of UI and other stuff, and is also more SEO friendly. However there is a cost involved. You have to spend around Rs 100-500 per year on the domain name and Rs 2000-3000 minimum on the webhosting.