I prefer usually challenging questions, while I may spend some time on easier ones trying to explain something that used to be difficult for me. This is not the most rewarding way to get reputation points, but this is how I like to answer stack overflow and server fault questions, when possible.
My preference goes to algorithms, and C, a language that I've liked and known for a long time, while I like also to visit server fault and its many interesting and challenging system, DB, nginx, ... questions and answers.
Linux has been my working environment for almost 10 years. And a (few) Mac for leisure.
As of now, I never gave a negative rating. This is the best way I found to move away the temptation to abuse the down voting ability.
Q&A for professional and enthusiast programmers
Q&A for professional system and network administrators
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Q&A for computer enthusiasts and power users
Q&A for people studying math at any level and professionals in related fields
Q&A for Ubuntu users and developers
Q&A for students, teachers, and linguists wanting to discuss the finer points of the French language
Q&A for passionate videogamers on all platforms
Q&A for active researchers, academics and students of physics
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
Q&A for power users of web applications
Q&A for power users of Apple hardware and software
Q&A for professional graphic designers and non-designers trying to do their own graphic design
Q&A for professional programmers interested in conceptual questions about software development
Q&A for linguists, etymologists, and serious English language enthusiasts
Q&A for Information security professionals
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Q&A for theoretical computer scientists and researchers in related fields
Q&A for professional and amateur chefs
Q&A for pro webmasters
Q&A for software developers, mathematicians and others interested in cryptography
Q&A for peer programmer code reviews
Q&A for students, researchers and practitioners of computer science
Q&A for serious players and enthusiasts of chess
Q&A for students, teachers, and linguists wanting to discuss the finer points of the Japanese language
Q&A for students and teachers of all martial arts
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Q&A for professional, enthusiast and amateur photographers