A rectangular table, the more traditional or the two, can generally seat more people. It can be the more flexible option, as it can be extended if it has leaves. Most people use rectangular dining tables, as they work well in long rooms, like most dining room areas.
Circular tables can be a great option for hosts with smaller dining rooms. Families with small children may like this option better as it has no sharp edges. Guests have an easier time interacting with one another since they can easily see everyone at the table. Many like this option as it provides a cozier, and more intimate atmosphere.