I would say Scour, because you can vote and comment and get points. It is more fun than an ordinary search engine.
Firefox is faster and more customizable.
http://lifehacker.com/396048/
Hmm, lets see. For me it varies alot. I visit and search for plent of new sites every day.
Firefox 3 do count visited times and ever since I installed it, the list:
1. gmail.com
2. firefox startpage
3. google.com/reader
4. meemix.com
5. Facebook.com
6. tyda.se
7. binero.se
8. docs.google.com
9. metrobloggen.se/codler
10. youtube.com