I have collies (one at the moment). I haven't had any other dog types, but have very good friends who do, and sometimes walk other people's and have them to stay while they're on hols etc.
Collies are different to other dogs imho. They are fiercely intelligent. I talk in sentences to my dog and she understands what I'm asking (way beyond sit/stay/roll over etc). Some of them understand verbs/concepts - not sure I'm using the right words - but things like 'take the ball to the teddy', and 'put the ball in the box'. This intelligence needs a lot of exercising, by you. They can also be prone to overthinking, which means that things other dogs just accept as 'that is what it is', a collie might think 'that's really unnatural, I must bark at that for hours'.
The other issue with their intelligence is that they decide when to obey. They are highly trainable, and you can get them to a point where they are 99.9% obedient, but literally every time you command them to do something, they decide if it's worth their while. They do like to please, so are obedient most of the time, but if there's that very tempting sheep up ahead / that favourite doggy friend over there, etc, they might decide that their wants trump yours on this occasion. They are not slaves to their obedience.
Collies require physical exercise yes, and it's very good that you live in the countryside, but mostly it's their brains you need to work out. They are happiest when they have jobs to do. Assume you are not going to work the dog with sheep or you wouldn't be on here asking! So maybe you need to do a lot of agility stuff or similar. Most collies wouldn't be happy sleeping in a corner all day while you work, even if you're in the same room as them. If you don't have a serious plan for collie 'entertainment' you will quite possibly end up with a neurotic collie, whose only purpose in life is to dig up the garden/bark at cars/chew his tail.
Collies are usually friends with everyone in the family, but they often pick a favourite. That will likely be you if you are with it all day. They might not properly obey others, or might just tolerate petting from the kids but not really enjoy it. They're all different in this respect though.
They are wonderful dogs if you know what you're doing, and you have the time and resources to look after them properly. Personally, I wouldn't advise anyone to get them as a first dog.
If your wants list is just no drooling/cleverish/not yappy, there are loads of great dogs to choose from! Any medium size dog will love long walks. If you're super keen to get a collie really soon, how about an older non-collie rescue (that's good with cats and ferrets!) to learn some dog skills first? Then a collie pup after?