Depends on the job you want them to do, the land and buildings you have and a host of other factors.
Rough grazers needing nothing more than a bit of hay in winter, to outwinter and produce a good calf every year - here in Cumbria you can't beat a Blue Grey (Whitebred Shorthorn x Galloway), we use an Angus bull on ours.
My own cows are Jerseys; I love to handmilk and use the milk, plus they rear their own and some bought-in calves - so they're good little workers, but hands-off they are not!
Are you asking out of general interest or are you thinking of getting some for yourself? If the latter, tell us more about the land, buildings, climate and conditions, and your own situation (full time or part-time stock-keeper, living on the land or a drive away, etc.)