Size is Important... _ You should be able to pick up and set down a cup without excessive bending or stretching. The average occasional table stands around 16┰ inches high. Then you have the length to think about. A table the full length of a sofa would be too long _ about 50 _ 60% of the sofa length works well. Round, square or oval it's really up to your personal preference, but if you want to be controversial, you can do a lot with angles and curves, and there is no reason why they cannot be combined. So lose the idea that your table must be rectangular, round or oval.
The size of your singular coffee tables is also a very important consideration. If you have larger scale furniture you want your coffee tables to be larger in scale also. A room can look odd and unbalanced if the coffee table is disproportionately larger or smaller than your other furniture. Keeping this in mind you should determine what size coffee table will best fit your space. You don't want to purchase a coffee table only to realize when you get it home that you don't have space for it because it's too big or that you have too much space because it's too small.