There are different traffic sources. But Organic traffic from search engines is the best and mot important traffic sources. It improves your authority and popularity.
Your question has an another answer: Google is the best traffic source.
Thanks, Munna Hossain
Actually it is kind of the other way around. Google does not improve your authority because you get traffic. You improve your authority and get ranked and then Google gives you more traffic.
Also in case you did not notice this thread is in the following section
Main Backlinks/SEO Discussion > Traffic Generation WITHOUT Google
which kind of leads to answers other than Google.