We have been looking into getting a dog for a couple of years now and have come to the agreement that this summer will be the perfect time to get a dog. We have been looking into getting a dog from a shelter, but unfortunately (or fortunately depending on how you look at it

) there are not many shelter dogs where we live or even in the area. We have therefore been looking at getting a dog from a reputable breeder instead, which of course would mean that we would need to have the time to train the puppy, which we will have from this summer.
We have of course been looking into some breeds ourselves that we feel like would fit into our family, but are having a really hard time choosing the right one. Therefore we figured it would be great to have a more objective view upon the choice.
What breed would you recommend for a family who:
- Are first time dog owners
- Is very active
- Have older children
- Live in a house with big yard (fenced)
- Live in a temperate climate (pleasant summer and mild winters with a bit of snow)
Some of the things we are looking for in a dog are for it to:
- Be of medium to big size (though not enormous)
- Like long walks and jogs
- Be able to be home alone 2-3 hours during the weekdays
- Be somewhat trainable (wont need to be able to learn a bunch of tricks, just need to be able to bring it to the basic puppy and young dog training classes)
- Be friendly, but give a warning bark
- Wouldn't mind one with a longer and thicker coat (not a deciding factor, just personal preference)
What breed would you recommend?