Yes Sub domains like blogspot or any not useful for adsense earning now a days they do not gives high click rates even u have dense and good niche ... so try any dot com or own domain name to get high earnings in adsense ... about traffic u can comment on it below ...
Of course they're no good as you can't get decent PR with sub-domains or anything like that. In fact, Google AdSense doesn't usually accept sites hosted from sub-domains.
I have a blogspot which i have maintained few year back and with few post and 250 visitors per days it still making 2.5 to 6 USD per day with out any effort.
blogspot is free even you got small earning, you no need to pay domain and hosting for me its better have 500 blogspot and earning $100 per days than have 50 website earning $100 per days but it back to your choice and strategy