Mendeley was the first program of this type I used, so it has the comfort of familiarity. I noticed that a couple of websites I visited have ReadCube embedded. So Im using Mendeley and ReadCube side by side for comparison. ReadCube is cleaner looking and prettier, but although Mendeley looks more pedestrian, I like to have everything there in sight rather than a minimalist design where youre not always sure where to find the function you want to use. The search engine of one may be superior to the other, but if so, its not yet apparent to me. It would be great if these programs could integrate with ResearchGate; now THAT would be a REAL timesaver. Finally, ReadCubes free online archive/sync limit is 300 Mb whereas Mendeleys is 2 Gb. Theres probably a way around paying for more using Dropbox or whatever, but its just simpler to pay for extra space.
MAFinOKC about Mendeley (PDF Reader)