One of the first things you will have to ask yourself is where you will be placing your dining table. A round table curiously seems to draw all elements that surround it towards it, thereby anchoring itself (and the chairs) visually more than a rectangular table would. It also takes up less space.
As mentioned, rectangular tables present a certain advantage in terms of capacity that round- and square ones do not. Imagine having to place all the diners to be seated at this elongated table at a round one – you’d have to have a pretty big round table!. For big dinner parties, it’s best to opt for an elongated/rectangular table, as you get more space for chairs and guests.