I've used both and prefer Wordpress myself, but both systems have plenty of pros and cons. It really depends on what level of "do it yourselfer" you are. Wordpress caters to people who want more control over their site, especially if they are self hosting. Blogger is for people who don't need that much control or don't know how to manage their own self-hosted site. I self-host my own site, and the template I use for my site is free and extremely flexible, but the biggest draw for me is the complete control I have. Few things make me crazier than wanting to do something and not being allowed to.
I've built websites for people using Blogger and Wordpress. Explaining Blogger to people is way easier than explaining Wordpress, so for newer bloggers, Blogger is probably the way to go until you want to venture into hosting your own site (if you ever do). Wordpress makes it very easy to export your blog from Blogger and upload it to Wordpress. You cannot, however, easily upload your Wordpress blog to Blogger.
While you can use Google Friend Connect with Blogger still, it isn't very important in the long run. I had GFC on my Wordpress blog until they killed it in March. Then I set up my blog to make it easier to follow by RSS feed, and my followers have grown faster than they did with GFC. GFC is a better visual reminder to follow, but you can grown your follower base either way.
Blogger is better if you just want a blog, nothing too fancy, and you're not interested in the level of control and customization that Wordpress has. If you want easy and user friendly, this is the way to go. It's out-of-the-box ready as a blog. For a more comprehensive website look, you usually need to hire a designer to put it together for you, unless you've got the know-how. But if you do, you'll probably prefer Wordpress.
Wordpress is better if you want to build more of a website instead of a blog. It's the way to go if you want control over everything and are comfortable with all that entails. For access to all of Wordpress's abilities you have to self-host, which costs money. Blogger only costs if you buy a domain name. Wordpress allows you to do "fancier" things, for lack of a better word, but that means it's not out-of-the-box ready. Wordpress has a free version but honestly I haven't used it for so many years I am not familiar with what it currently offers.
In the YA world, who uses what service runs the gamut. Blogger, Wordpress, and LiveJournal are all pretty common, although I've seen a handful of authors abandoning LiveJournal for the other two services lately. I've also noticed that group blogs tend to be run by Wordpress, because their group blog options are better. Many of the group blogs also look like they've had a pro designer work on them, but I don't know that for sure.