The smaller the dot-pitch, the sharper the image...but it's directly proportional to the size of the screen. If you have an 800x600 display that has a dp of .25, it will look better than one with a dp of .30. However, if you have a .25 1024x768, it can actually appear comparable to the .30 dp 800x600.
Generally, you want the lowest Dot-Pitch in the screen-size class, with the lowest response time available.