aptitude vs apt-get

[MacGoose]

I've been using some of The Perfect Server howtos for Ubuntu. Specifically the 10.04 and the 11.10. In 10.04 aptitude is used throughout and apt-get is used in 11.10.

In my understanding aptitude is the new and prefered one and apt-get is old and outdated.

So why does an old howto use the new aptitude and the new howto use the old apt-get?

Anyway. Should one use aptitude or apt-get?

My main server is still 10.04 as it is LTS.