I think the choice of the blogger platform is depends on you. If you want to get high traffics towards your blog then you should choose the low pr and high traffics platform. I think the free blogger platform also have high pr and getting high traffics.

which one getting better ? PR usually following by it traffic, more traffic = more popularity and it can grow up your PR, i think low PR with huge traffics is better and more easy for beginning, after that is your home work to manage for SEO and drive a lot of traffic for your site, when Google update it PR your site will be in good position..

Blogspot or wordpress.com ? is depend on you, i think both of them have advantages and disanvantages