If I were you, I'd get a mongrel. They tend to be healthier and live longer. The dog that I grew up with was a mixture of poodle, Irish setter and schnauzer, and she lived to be 19 years old.
I wouldn't recommend a large dog. You'll end up paying a fortune in dog food, and large dogs can be hard to control when they're younger and full of energy. But I wouldn't get a small dog either. They tend to have fear issues around other dogs and often overcompensate with agression or permanent barking. Small dogs are also more prone to health issues, behavioral problems and hyperactivity. I suggest looking for medium-sized mutt
If you adopt a dog from an animal shelter, be prepared for high vet bills. Animals at shelters are often very stressed, might be malnourished due to food competition, and usually get only cheap food or a very irregular diet due to different brands in food donations, which weakens their immune systems. They also live on a small space with lots of other animals, which is a perfect breeding ground for diseases. And you never know how often a pet has been adopted before. It might be a problem animal that several people have adopted and brought back.
One of my cats is a rescue, and although I love her to bits, the first months were a total nightmare. She had a tapeworm and roundworms -- they assured me that she was wormed, but that was either a lie or she had caught worms again from another cat -- a bad cough and short breath (probably from worms in her lungs), a giardia infection, and constant diarrhea. On top of that, she refused to take her meds and infected my other cat with her giardiasis and diarrhea
Giardia are extremely difficult to get rid of. I spent all day disinfecting litterboxes and toys, washing blankets, cleaning carpets, and trying to somehow get the cats to take their antibiotics.
I don't know if I would ever adopt a rescue again after this experience. You also never get a rescue to trust you on the same level as a pet that you've raised yourself, which makes it harder to give them medication or take them to vet (although that should be much easier with a dog). On the plus side, difficult environments like shelters often make for highly intelligent pets. My rescue is scarily smart
I agree with this and would add...if it were me get it from a shelter since these dogs are more likely to be put down vs a pure bred dogs in a pet shop. These animals sold into shops are not likely to be put down since there are a lot of people willing to buy one. Then again there are many people who admire pure dog breeds. There are few pure breds that may not be so bad like the yorkshire, shitzoo, cocker spaniels. I love labs but I hear that a lot of large breed dogs as well as very small ones are not very healthy. Might want something that you know is a breed but has a mix like maybe a lab mixed with another nonagressive breed such as the golden retriever. Also imo you can't always trust how a breed will behave all the time. I don't know if they have a lot of programs aside from fostering animals...where one person fosters a pet and lets the person who is interested get to know it better and see how it will behave towards you and other pets you may own. It'd be nice to know what kind of dog you're getting before you automatically get it at a pet shelter. I still think a mutt is much healthier. I as well as my grandmother have had to watch pure breds like the akita and mastiff die too soon for their time. It was especially sad when the Akita my grandmother gave me died at just 3, she was a very beautiful dog. However the mutt I had who was both a lab and chow mixed lived a very full life. So be careful if you do decide to get a pure bred.