The rectangular tables are the most common, which shows that they are a practical, functional and comfortable option. They are perfect for elongated dining rooms and they allow for more diners in less space. In a small room, a rectangular table can be shoved against the wall and still be perfectly practical.
The style of table you have selected will directly impact on which chairs will work. For example, you'll often find that circular tables can accommodate far wider seats and even high backs will work well, wheres more angular designs often require compact chairs, as they'll have legs to contend with.