] Not being a farmer, I do not know whether it is easier to drive a team of horses or a team of oxen, but as horses are still used, I guess they are better at the job.

Depends. In the early Middle Ages, horses outproduced oxen on the farm, but also were more expensive to use. The return was roughly the same for each animal, so there was no incentive to use the horse. Some unknown genius invented the horse collar around, what?, the eleventh century?, and it was suddenly evident that horses hadn't fared so well because the previous methods had restricted their breathing. With the new collar resting on the shoulders, horses could return at least twice as much as oxen could for their keep. So it's all in how you hitch the plough (as well as various factors like the wetness of the ground, size of the hoof, quality of the feed, etc.).

YHOS,
Snarkhunter