after achieving a pr of 3 on my site, after nearly 10 months I have recently achieved a pr on blogger neeshu30.blogspot.com though the pr is one. Not to mention, I produced a nice traffic only in the last month rest the site was nearly dormant and had only 10 posts. I think blogger has drawbacks like you can't manage your content so well, only you are allowed to post, lack of category, poor web interface, lack of templates. I think wordpress is better have a great day keep trying you will get a pr have fun enjoy
You need to host your own wordpress blog so you can add adsense and other programs. Wordpress is easier to get ranked well if you work on it.
I suggest you buy your own domain. When you will build backlinks; you will be building them for a sub domain of blogspot not your own domain. Instead of blogspot, why not own your own domain, so that you will be building backlinks for your own site?
You can use your own custom domain in blogspot too but it is always better to use your own hosting with wordpress if you are serious about it