I have used both, and personally, I have found more success with Tumblr.
I found that I get more traffic with Tumblr - this is from following a lot of similar blogs and liking posts and such. Maybe it was just me, but I didn't find much success on Blogger, plus I felt a bit isolated on there - like my few readers (numbers were pretty low) wouldn't comment or anything.
Plus, I find that I'm better able to connect with other bloggers and my followers. They always joke about Tumblr being a family and I completely agree. I have met some wonderful individuals on here :)
I also love how customizable the Tumblr platform is, and that you can choose from so many looks and layouts for your blog.
I actually wrote and published a Hub on here talking about the reasons why I love Tumblr.