In my opinion, it just depends on what you're looking for.
If you're just looking for a way to market something, instagram would be good, but if you're looking at a range of goods, i think tumblr would be better, simply for the layout.
If it's personal use, then again, It depends what you want to do. Tumblr is excellent for creating huge picture blogs like mine (letsfucktheworldandallitstrend - if you're interested) and also some info blogs. It depends on which layout you use, and/or if you're willing to pay a little extra for a premium theme.
But Instagram is good for simply browsing photos, and sharing photos with friends. Tumblr is less for friends in my opinion, as blogs are often more personal. I only have 4 friends on my tumblr, out of my 120 followers...