Thrown with proper mechanics, the four seam will be the straightest, flattest and fastest pitch. However, the speed difference in a four seam and two seam may only be a mph or two. Often it is not a big difference. Depending upon the individual pitcher, there may be no difference in control.
The two seam should tail in a little when thrown by a RHP to a RH batter.
A two seam to the bottom inside corner (again, assuming RHP & RH batter for illustration purposes) can be a very effective pitch. Ditto for the four seam angled to the outside corner. A four seam angled up & in on the batter's hands can often result in a pop up. A four seam throw on the inside and a few inches above the top of the zone can get a batter chasing the pitch.
Think about the movement of the different grips.
Then think about the batter's characteristics (e.g., RH or LH, stance, stride, swing, etc.).
Then think about the situation and the desired result.
These things will factor into your pitch selection. If you would like some additional info on pitch strategy and selection, just let me know.
A good two seam, four seam and changeup will take you a long way.