Well i guess dentistry you know what job you're signing up for, whereas medicine has many different options (though i will steer clear of saying its more varied - you can only pick one speciality and many are extremely repetitive). So i guess you have to decide whether you like the sound of being a dentist or not. If you do, dentistry offers quicker training, more independence, potentially better working hours, and i think probably less bureaucracy although they are tied down by complicated NHS payment schemes a bit i think. Don't know how pay compares - probably varies more than the rigid structure of medicine.