In terms of gaining a place on an undergraduate course the applicants:places ratio is highest for veterinary science, then dentistry, then medicine.
But thats not to say its easy to do medicine than veterinary science, because nthe application procedures are different and also someone applying for veterinary science will not be applying for medicine (if they are something is sadly wrong!!!)
Grades are pretty much the same for all three now, but only play a small part in getting selected for one of the courses.
So who is more qualified, well as I said before a vet is most qualified to treat animals, a dentist most qualified to treat conditions of the oral and oro-facial region, a GP genral medical conditions, and a surgeon the surgical conditions which are in the remit of their surgical speciality