Observer
2 websites

Observer is free to use

http://observerapp.com/

Observer is a web analytic tool developed by Ludwig Pettersson. Observer also includes a toolbar that lets you view your analytics no matter what site you are on.

VS

Rich
1 websites

Rich offers both free and paid options

http://www.richmetrics.com

A campaign analytics tool for digital media focused on creative agencies, that gives them all the metrics they need - and nothing they don't - on one simple report page. The first tool to answer critical questions such as was the ad visible...

Market Share by Top Websites

2 In terms of market share, Observer is clearly lagging behind, losing to Rich in all segments.

Websites Categories

1 Observer has better usage coverage in more websites categories. Including Computers Electronics & Technology.

2 Rich hasn't got a lead over Observer in any websites category.

Geography

1 Observer is leading in most countries, including United States.

2 Rich hasn't got a lead over Observer in any country.