This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
It depends on your requirements.
Apache is widely popular Server Software.
But several popular websites (like Youtube and Wikipedia) use lighttpd. Lighttpd doesn't have all features which Apache has, but it's known to be fast.