I think the answer to this really depends on you. I adopted a young and very highly energetic and athletic dog one time when I was living in one room with no yard in a huge city. It worked fine, but only because I genuinely wanted to spend time doing energetic and playful things with the dog every minute I was not working. We had two one-to-two hour walks every single day, regardless of weather or my energy level. Frisbee sessions once a day. We went hiking all day one day out of every weekend, and at least once a month we went out of the city and went camping in the wilderness for the weekend or for a long weekend, and hiked every day there. I spent a half hour every day doing training with the dog.
None of this was hard for me because, as I say, this is what I really wanted to spend my time doing. But I think if I had not wanted to do all that, and had therefore gotten slack with it, it would have been a serious detriment and disservice to the dog.
My advice is to think this through very carefully and ask yourself how much time you are able to and more importantly really want to devote to making sure the dog gets the exercise he needs. And then choose on that basis. If you have less time to devote to the dog, maybe a smaller dog would work for you simply because they cannot go as far and exercise would then take less time.
Also, please consider going to your local shelter or to a rescue group and getting your dog there. There is no need for a purebred, and you may find your perfect match in a dog who is in need of a good home.