Of the 90 or so native British sheep breeds, we have chosen to keep Hebrideans. They are a hardy primitive sheep from the Northern short-tailed group and probably originated on the island of North Uist potentially as far back as the mid 1700s.
Our farm ranges up to over 1000 feet above sea level and in winter can see temperatures plummet and snow drifts many feet deep. The fields are steep and sit just below the moorland line, so have acidic and often wet ground. This makes it difficult to use machinery and there are large buffer zones at the top of slopes and beside the dry stone walls where it isn't possible to mow. As a result the grazing can get thick.
It was essential that we chose a breed that could cope with the conditions here and would graze even the rougher vegetation.
My thoughts on choosing a livestock breed, including sheep, go as follows:
Make a list of all the breeds that will thrive (or at least survive!) in the conditions (environment, grazing, climate etc) you have.
Narrow down this list to the breeds that are most suitable for the end product you want (e.g. meat, wool, fleeces, lawnmowers etc).
Reduce the list to breeds that you can physically manage (e.g. handling to check feet/drench/inject, shear etc) and have the facilities for (e.g. winter housing if needed).
Go and see the remaining breeds at the shows, speak to their owners about the realities of owning them and get underneath the hype where everything claims to be an easy lamber/immune to foot or fly problems/great mothers/milky/the best meat in the world etc. Prioritise your list for the characteristics that matter most to you.
Pick one (or more!) of the breeds left on your list based on what you like the most and would enjoy seeing out of the window on a sunny day and will be most willing to trek across a muddy field in the driving wind and rain to check up on.
Our initial list had quite a few breeds that could do well on the farm. We knew from ordering some Hebridean mutton online that they tasted good. They have an attractive fleece (far more interesting than your standard "white sheep") and are smaller and lighter (so theoretically easier for us to handle, especially important as we don't have much machinery and jobs like shearing are done manually). Their ability to live out all year round and even lamb outdoors in harsh weather was essential as we started with very limited outbuildings. Ultimately the choice came down to a couple of breeds with some pros and cons for each, but the fifth point was the decider and it hasn't changed - looking out of the window at the flock is always enjoyable (except when none are in sight and panic sets in that they have escaped) and spurs you on even when facing a trek against stinging snow being blown by gale force winds in order to dig out snow drifts piling against the walls so that the sheep don't get buried.
All our flock are birth-notified or pedigree registered with the Hebridean Sheep Society whose work has helped the breed move off the Rare Breed Survival Trust's watchlist.