The space that your dining table inhabits should have a natural impact on the chairs you choose. For example, if you have a tall table in a contemporary kitchen area, you might prefer some tall bar stools, to give a breakfast bar look. Whereas, if your table is in an open-plan room, you'll want chairs that align with your sofa choice and other decorative touches!
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.