Depends on how much you make use of the social element of DropBox. Friends, Family, Colleagues, coworkers all share their files with me through DropBox shared folders. About six months ago I finally bit the bullet and just bought a subscription.

For whatever reason, I've never had a folder-share request for anything but Dropbox, and, it's performance has been flawless for me across all my systems.

In comparison, photostream, which only needs to sync across a limited number of platforms, all controlled by Apple, has been consistently unreliable, and i frequently have to hop into my iPhone Photo application to get it to sync pictures over to my Laptop.

Syncing is hard. Dropbox has it nailed. I have zero desire to mess around with anyone else in the near future, so, they've won as far as I'm concerned.