Everyone has a different standard raise, mine started at 4X, as my raises generally meant good cards, and it was in an effort to drive people out of the pot. As my game improved, I opened up my pre-flop play, more of my raises were with the intention of stealing the blinds. The 3X accomplished nearly the same thing as the 4X, but was less risk for the same reward.
Controlling the pot size is also a critical aspect to poker, a 3X raise keeps the pot smaller if one were to get callers as opposed to the 4X.
As a tournament reaches it's later stages, my preflop raise amount goes down to 2.5 to 2.9 times the big blind, as it essentially has the same effect as the 3X.
As a side note, tournaments with antes involved and saavy players sometimes requires a larger preflop raise than 3X, as the pot is larger to start out and a good player may call with a wide array of hands getting very nice pot odds.
Hope that helps.