We keep Dexters and Highlands.
Dexters, being small, readily available and cheap, are what a large proportion of smallholders start with.
However the Highlands are much more docile. They are incredibly easy to keep. Being a largely unimproved breed, they have a digestive system 30% more efficient than most other breeds, so do not need concentrates, but can fatten readily on forage alone.
They are fascinating animals and have a definite herd hierarchy. So the top cow is always the first to eat and drink. If she approaches, the lower order cows will move away to make room for her. So if you have a feed ring with 12 spaces, you will only get 2 cows feeding at any one time, one at each side. We have about 10 highland cows and use 3 feed rings so they all get a chance to feed, otherwise the ones at the bottom of the pecking order will have to wait hours to feed once a new bale of hay has been put in. The funniest thing is if some of our dexters are in with the highlands because the dexters don't recognise this pecking order. So when there's a new bale the dexters just push in and start eating, and nothing, but nothing will shift a dexter till it's had enough. The highlands get very put out by this as it destroys their system and they can't understand that a dexter is completely unintimidated by their horns.
So having said that, I must admit the highlands are my favourite every time.