Ripley has a point in the motherboard size. Another thing apart from more slots is cooling: A full size board can afford more space between the built in components, each of which produces some heat. And it's also very true that a full size motherboard will fit nicely into a mid-size tower, still leaving plenty of room for airflow. The crucial thing to consider is the depth, not the height, because of the length of some video cards.
My experience with Gigabyte has been positive so far, as is the case with some of my computer savvy friends. I must admit, though, that the Gigabyte mobos in question are/were pretty old. My current one has served for seven years and the others were much older. Most of the salvaged lot found a new life with Linux, the builders being very happy to get exactly Gigabyte.