Many people choose a 401k because it is what their employers provide and they have never heard of an IRA. However, the assets in an IRA are currently growing faster and have a competitive edge over 401ks for a variety of reasons.
If your company does not offer a 401k match program, you may want to consider an IRA because it will grow more quickly. Your 401k, on the other hand, will grow faster if your employer has a match program where you get double what you put in.