Okay, I really wouldn't consider Tumblr as a blog site... That said, livejournal is still around and I know a few furs who use it. Wordpress is probably king right now of the CMS/Blogging website world. I use wordpress as the engine for all of my websites. Blogger... Well... Meh, it's just there. I'd say go with wordpress.

How simple is it to use? As in, can someone with not much blogging/website making experience make a professional looking blog, or will it look like something a child made?

Wordpress can be a little complicated at times. But if you're running it off their website instead of your own web server, it's pretty straight forward. You basically pick a thing you like and then just arrange the pages and content you want on the pages. It's more in depth when you're running it on your own server, you can do way more. But for simple blogging, using their site works best.