What I take out of it is:
- each company provides an influencer identification service
- all seem to rely on twitter, rather than other social spaces
- Kred seems slightly more accurate than the others looking at the types of things it measures
- if you play the game i.e. engage with the three tools, you get a higher score
Overall, most of them gives you a good indication of influence of someone you are looking at to involve in a campaign, but IMHO I wouldn't rely on the tools to give a definitive list of the people who influence a certain subject.

