Client Side or Server Side tagging?
Lots of debate happen over what is the best approach to capture the site analytics data. There are 2 approaches Client-Side tagging(GA, WT, Omniture all depend on this). Then there is server side tagging.
My take on this is a Hybrid approach is the best solution.
Most of the information below is readily available online. If you need more information see here http://www.ecommercetimes.com/story/49264.html?wlc=1292269237
Client-Side Tagging:
Client-side tags capture data only for the pages you want to track. This reduces the amount of data you have to store or process. Client-side tags also act as an automatic filter, because they don’t collect images and other kinds of hit data that you don’t want to collect. This automatic filtering also helps reduce the size of your data files.
Because the script runs each time the page loads, client-side analytics software gives you accurate visit and page counts, even when pages are loaded from a caching or proxy server. Web server logs can help you obtain IT-based metrics such as spiders, downloads, bandwidth and errors. Client-side tagging can also help you get metrics like screen resolution and the number of Java-enabled browsers.
Client-side tags require additional hardware to run the data collection server, unless you use a hosted version(ASP). Client-side tags also require time or software to embed the script in each page you want to track.
Likewise, if a redirect page does not contain the script, it will not get counted. This could be crucial if you are using redirect pages to track advertisements. What’s more, downloads are very difficult to track with client-side tagging.
The crawler or spider does not run the script,its visit is not captured. Without custom configuration, client-side tags only capture HTML pages.
Server-Side Tagging
Since most Web servers generate Web logs, they are typically easily and immediately available, making server-side Web analytics advantageous to the end-user. Server-side analytics offer lots of IT-based metrics, such as reports on spiders, downloads, bandwidth, load-balancing and errors.
You don’t have to decide in advance exactly what data you want to report on. Web server logs allow you to go back to the raw data at any point and change what you want to analyze, as long as the fields in the raw data were being logged initially.
Server-side solutions could be seen as more reliable because every page view requires a log entry, but there is a lot of information that is collected by client-side that can’t be collected by server-side analysis.