Server Log – stores information when requested from a site .
Record kept at the server level that records each file requested from a Web site.
Coded page –
A technique in which a small image, usually a 1-pixel transparent image (called a pixel tag or transparent GIF), is placed on a Web page. Used in conjunction with a cookie on the user’s computer, the image returns data about user activity on the Web page.

Which is most useful

Trafficis measured by
Hits, impressions, page views / deliveries, Sessions- length of time spent, Click throughs, and audience.
Audience is measured by
Total vists, return and unique and anonumous and registered users,
Behaviour on the site page views, seesion time, path in and out of site entry page/landing , shopping abandonment,
Campaigns are measured by
Communication channels, e-mail, banners etc. Offer follow through, and search /keyword use.

Other Frequently use metrics are
• Average number of visits per day
• Number of page views per month
• Average visitor session length last month
• Number of hits for each hour of the day
• Paid search results for the most recent 7-day period

All options are good but the question is what is the goal. One must understand what he/she is trying to accopmlish to come up with the proper mix of metrics.