I raise AQ preflop from anywhere but I play 10NL so people play alot of weaker Aces. It also defines the hands you are against if someone reraises you. If you limp and they raise they could have AJ or maybe even AT/KQ but you still have to fold really. If you raise and they reraise they dont have AJOn really passive tables where people are limping AK, QQ sorts of hands then ill limp. Ill also limp if i know people will play Ax like the nuts when it hits an A but wont call a preflop raise with it. I prefer to do this from position though (and even then its very rare) so i can control the pot size a little better.
I almost always raise AQ preflop but fold it to a reraise from anyone who isnt a maniac.