Round are the most valuable. Perfectly round Pearls are difficult to find. Semi-Round Pearls may be shaped like Buttons, Pears or simply not round. They are smooth but not truly round. They or more valuable than Baroque but less valuable than Round.
Baroque have irregular shapes including bumps or arms.
The important thing to remember is the Pearls should be similar in shape from one end of the strand to the other. 2mm is a small Pearl. 8mm and larger is considered vary large. Freshwater Pearls are measured by length and width because they are not round. Generally the larger the size the more expensive the Pearl.