A 60" round table seats 8 comfortably. Linen sizes would be a 90" round to fall halfway down the table and a 120" round to fall to the ground.
A 48" round table seats 6 comfortably. Linen sizes would be a 90" round to fall three quarters of the way down the table and a 108" round to fall to the ground. This table is a good cake table as you have room for the cake and serving plates, napkins, etc.
A 36" round will seat 2 comfortably. A 108" round linen will fall to the ground and puddle a bit. This table is frequently used as a sand ceremony table.