A raise pre-flop for me depends on many factors such as: how many people at the table, your position, what has happened in front of you, how the table is playing, etc.

I generally re-raise with AA or KK (regardless of position) and also never limp in with these hands. A high pair is likely to be the best hand pre-flop and doesn't really need to hit the flop. AK or AQ on other hand are drawing hands and usually need to hit the flop. I will usually limp in with these in early position and raise on the button.

And I also believe the answer to your question is a matter of your playing style. Some people are very aggressive and some are tight and passive. I suppose the absolute best stategy would be to be able to adjust your game according to your opponents.