Google doesn't disclose what niche is better or what click through rate is on average. You need to test your own. There is very little averages with Google Adsense. Typically the average click through rate (CTR) is low. 10% is high.
I requested all members who want to join my groups on other networks (e.g. LinkedIn) to first sign-up with my Ning network, in order to be accepted. I don't have the time to check if all potential members follow my rule, but it significantly increased the number of sign-ups on my Ning network, and also help reduce the number of people who join for spamming purposes.