Debian Apt Sources List Generator
Personally, I prefer stable with backports. Testing is also good but still update might introduce critial bugs sometimes. It is not easy to maitainly a stable and update to date balance. You can certainly use multi-sources, i.e., use stable, testing, sid and experimental at the same time. multi-source is much harder to maintain especially when you want to support multi-archi It is not recommended.
deb http://ftp.us.debian.org/debian stable main contrib non-free
deb-src http://ftp.us.debian.org/debian stable main contrib non-free
deb http://ftp.debian.org/debian/ wheezy-updates main contrib non-free
deb-src http://ftp.debian.org/debian/ wheezy-updates main contrib non-free
deb http://security.debian.org/ wheezy/updates main contrib non-free
deb-src http://security.debian.org/ wheezy/updates main contrib non-free
# stable
deb http://ftp.us.debian.org/debian/ stable main contrib non-free
deb-src http://ftp.us.debian.org/debian/ stable main contrib non-free
# stable Security
deb http://security.debian.org/ stable/updates main contrib non-free
deb-src http://security.debian.org/ stable/updates main contrib non-free
# stable-updates, previously known as 'volatile'
deb http://ftp.us.debian.org/debian/ stable-updates main contrib non-free
deb-src http://ftp.us.debian.org/debian/ stable-updates main contrib non-free
# stable-backports
deb http://ftp.us.debian.org/debian/ stable-backports main contrib non-free
deb-src http://ftp.us.debian.org/debian/ stable-backports main contrib non-free
# testing
deb http://ftp.us.debian.org/debian/ testing main contrib non-free
deb-src http://ftp.us.debian.org/debian/ testing main contrib non-free
# testing Security
deb http://security.debian.org/ testing/updates main contrib non-free
deb-src http://security.debian.org/ testing/updates main contrib non-free
# sid
deb http://ftp.us.debian.org/debian/ sid main contrib non-free
deb-src http://ftp.us.debian.org/debian/ sid main contrib non-free
# experimental
deb http://ftp.us.debian.org/debian/ experimental main contrib non-free
deb-src http://ftp.us.debian.org/debian/ experimental main contrib non-free