I am trying to decide which one to use for a small-medium site, but also want to be able to scale the site and the analytics along with it.
Thanx
Let me know
A more fundamental decision point is understanding what kinds of information you want to track:what metrics are important to you? You're at much greater risk of having an analytics package that doesn't help you answer meaningful questions in an actionable way than having one that won't scale. Google "pirate metrics for startups" for a little more insight.
Also, you may want to explore one of the several "alternative" metrics packages, those that are better turned to funnel analysis or whatnot than either GA or Omniture seem to be.