The Handcrafted theme is both simple (just one fixed column) but it's also visually quite rich and warm. It features a responsive design on the homepage, an increased engagment by showing your latest publications at the bottom of each post and a special optimized reading option.
Silk is a minimalist template with a grid layout. On the left lies a dashboard which displays the description of your tumblog and lists your personal pages. Silk also is SEO-compliant by generating proper keywords for each of your posts. Also permalinks are optimized for all kinds of medias.
The Journal Theme was made for those who wish to have a retro-looking website/weblog or for people who want to start a public or private journal. It supports comments via Disqus, social features like a Twitter widget and an increased engagement by showing your latest publications at the bottom of each post.
I have decided to play around with the Cargo theme and turn it into a photoblog template. Overall, the layout is inspired by traditional photo blogs or by the MobileMe Web Gallery. The theme was specifically thought for photos. If you intend to post other kinds of medias then it will probably not suit you, unless you tweak it.