iStock is so much easier with DeepMeta - if you upload to iStock and you're not using it then do check it out. It changed my life!
Easiest for me has to be 123rf - no categories and simple MRF attachment. After that, CanStockPhoto, CS are easy too. Mind you, the good news is we've just employed someone to do all this for us - yay!! :-)
DeepMeta was great relief. It really makes life much easier. Too bad it doesn't work for audio files. I had hard time yesterday uploading 2 audios. I had to fill all data 2 times for each audio because all data disappears when you make a mistake and write one keyword two times for example.