What is better, Google adsense or banner ad exchange sites ?

[wazir]

Google only pays you when visitors click on the adverts. The amount you get is a percentage of what an advertiser pay google for putting its advert on websites.You can get anywhere from 1cents to may be a few dollars, you can't tell. It's a good idea to have more than one revenue stream for your website but judging from your info you get approximately 80*30= 2400 visitors per month and your yearly visitors may not get near to 100,000 visitors for the year so I will advice you to stick with adsense. If you get a click through rate of say 2% of 2400/ month, that would make 48 visitors clicked on the adverts. You have more chances with adsense than with the banner exchange.
But remember that adsense amount is dependent on what the advertiser pays google for it.