If you have one formal and one casual dining space, you can really go to town with different chair designs for both. A casual spot will do best with sociable, comfy seating that naturally leads to conversation, whereas a formal setting is where you can play around with luxury fabrics. If you only have one dining room, you're going to need to combine all of these elements in one set of chairs, if possible!
For a more interesting and unusual style of dining furniture, rustic bench seating should absolutely be considered, as it offers a beautifully unique aesthetic. Easy to combine with regular chairs, for a little diversity, bench seats are ideal for busy family homes, where the evening meal is considered to be a cherished moment of reflection and interaction. Children always enjoy a more fun style of furniture and with a bench seat, there's always room for one more guest.