I was about to suggest … why not both? Flickr is just a good repository of all things photo, and it’s easy to grab a link from there to post into Tumblr. It’s somewhat of an “extra step,” but I don’t really consider Flickr social media. Is it? I guess.
If you have to choose, I’d go for Tumblr. The following/liking/sharing aspect of Tumblr makes it easy for your work to be seen by lots of people. I feel like Flickr is a little less integrated in that respect, if you know what I mean.