My mare is considered to be the old fashioned type, they are generally shorter and stockier than the more modern sports horse types and my mare has quite a big head too with a full sized bridle on a 14.1 body.(some of them have very arab type dished profiles these days. My mare takes 6ft 3 rugs which at her height gives you some idea of her body size. Different judges like different things but I would say that the in-hand classes are generally dominated by the more traditional cobs whilst the ridden is more variable, again depending on the judges preference. If you're looking for photos of more traditional examples have a look at Danaway, Trevallion, Llanarth stud just of the top of my head, if you want the sportier type then Derwen, Mayesmenach, Sydenham cobs seem to more often fit that description. All good in their own right and great at what they do so no right or wrong about it at all and if you are thinking of showing then check out the judges preference before hand as many will also be breeders so you will have a good idea what they are looking for.
Showing wise my mare has done extremely well at County level under saddle and in-hand, she drives as well but I've never shown her in harness.