Rectangular ovens are usually higher mass than circular pizza ovens, and are ideal for serious bread bakers who plan on making multiple bakes of bread on each firing. Because of their high mass, they are more suited to the lower temperatures of bread baking. You can get a high mass oven up to pizza temperatures, but not easily and not for long.
Circular ovens are best for pizza. Their fast, efficient heat up means that firing isn't an all-day, all-wood pile operation. They can, however, do enough baking needed by home users.
We have several barrel-vault oven users here. Look around. You might want to start with James' little essay on
round ovens (Why Italian Wood-Fired Ovens are Round).