Answers
LinkedIn.com - 5
Size of user database and clarity of connections in your network
I already have a profile with them and I've achieved good results so far.
Users enter their own information
its simple
The user maintains his own information and contacts
Spoke.com
Jigsaw.com - 2
Simply jigsaw is the best as you get all kind of filtered data as you like. even though there are concerns of inaccuracy, still I believe they provide around 67% accuracy?
Has direct email and phone numbers.
