I have to say I love our Shetlands! One hates people, but the other is wonderful. They both came in being scared. Their lambs are also friendly. they are much easier to handle because of their size. I look at full sized sheep and shudder. They are also great because of their naturally short tails clean face and legs, and they can be plucked instead of shorn. We haven't done this as we didn't know about it until they had been shorn, but we may try it next year. When we buy more I will be buying registered sheep. Personal preference really.
When we got our ewe's they had already accidentally been bred to a Romney ram. We were a bit worried as the lambs may have been too big. One ewe was fine, the second we had the vet in for. Both were long labours so we wouldn't voluntarily breed a larger ram to a Shetland.
Some other small sheep are Baby-doll Southdowns, Black Welsh Mountains, and miniature Cheviot around, at least in the US.
Good luck!