Business advertising

First of all, I need to make clear that I have no commitment by promoting Google Adwords, the pay per click search engine from Google. I am not Google affiliate at all. I just consider Google Adwords the most effective pay per click search engine and I will explain why.
Reason 1:
The Google audience / user base has traditionally catered to technical audiences and more importantly, to Internet savvy users: the kind of users who are comfortable with buying online. These users (the tech-savvy, buying kind) are more likely to use Google than Yahoo or MSN.
Reason 2:
Google Adwords delivers instant results. You can have your ad campaign up and running in 10 minutes flat. Compared to this Yahoo can take anywhere from 2 to 5 days while they manually review ads.
Reason 3:
With Adwords, you can target your prospects geographically down to countries, states and cities. This is a great advantage for businesses selling physical goods or localized services . They would prefer local prospects as opposed to someone half way across the world.
One exceptional quality about Adwords is that it rewards good ad performance. This is, for an ad that converts (clicks/impressions percentage) exceptionally well (high click through rate), your ad will get better ad placement as well as better pricing. Google wants to display the most relevant ads for the user. So, it makes perfect sense that you will pay less per click, the higher the click through rate of your ad is.
Click through rate is simply the percentage of clicks on your ad divided by the number of impressions on a particular keyword. For example, if 100 users saw your ad, and 2 people clicked your ad to visit your website, your click through rate would be 2%.
Google reports the click through rate for each of your keywords, hence the necessity of constantly monitoring the keywords performance for the continuous refining process until reaching an optimal performance of your set of keywords. This is an ongoing process, as you don’t know in advance which keywords are the best performers from the conversion standpoint.
Reason 5:
Your competition cannot see the exact amount you're bidding for your keywords or the CTR your ads are getting: a distinct tactical advantage that Yahoo lacks. Basically, your competition will never be able to tell how you are marketing your product. Although, Google has a nice tool to estimate the price your competition is paying for your selected keywords, this is called The Traffic Estimator Tool, found within your Adwords account.
Basically you set a maximum bid for your selected keywords and Google will estimate the expected amount of traffic for that keyword based on that bid. This is just an estimation as the final price paid for a certain keyword will depend upon the bid and click through rate of that keyword.
Reason 6:
Google provides a Quality Score for each of your selected keywords. Using its internal algorithms, Google scans your landing page and determines how relevant is the content of your landing page in relation with each of your keywords in your Ad Group. Therefore, by selecting and grouping related keywords and matching your landing page with these keywords, you can get a good quality score for most of these keywords. This in turn, will improve your click through rate and the price you pay for each keyword.