The conversion rate on GoClick is poor and it can take forever for you just to spend 50 dollars on clicks. Their customer support takes to long to respond and sometimes never get back with you. I would suggest to stay away from them and other small PPC and just stay with Overture and Google, they both easily reach most of the web.
Although I'm new to ppc marketing, I can share my impressions. Simply put, I received lots of hits through both goclick and google adwords, and both systems are easy to use. The mandatory minimum at goclick is a bit of a nuisance for me, tho, and when I started using google I stopped using goclick for several reasons. Flexibility with the amount I spend is one. Also, with google, I get more traffic for less money spent, and I'm more confident with what I hear from others about google.