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.
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.