I normally recommend rescue greyhounds, but they tend to be couch potatoes so might not fit the 'moderately active' requirement.
Golden retriever/poodle crosses (groodles) are great, and would fit your requirements perfectly. There can be a long wait time though.
Re purebreds vs bitzers, it's not always clear cut & depends hugely on the breeder. Lots of bitzers are bred for the pet trade by puppy farmers who will breed any dogs with the requisite bits regardless of temperament or genetic issues. Also, you want a breeder who will take the time to socialise the puppy from a young age. Rescue dogs are better from an independent rescuer (make sure the rescuer you adopt from demands the right to interview you, inspect your place etc before adopting, cos that shows they give a shit) or from the RSPCA cos the RSPCA put down dogs with problematic temperaments rather than put them up for adoption. Beware the ones who arrange to meet you in a park or something to hand the dog over, that's a scam, they'll demand big $ on the spot for the puppy & threaten to kill it in front of you & your family if you don't pay. Some purebreds have well known tendencies towards genetic problems (king Charles cavaliers, golden cocker spaniels, bulldogs, pugs, German shepherds for example) so if you want to get one of these it's best to pay the extra $ and get one from a top breeder. Most purebreds are no more or less prone to genetic problems than a non-purebred but there are some landmines, do your research first. Ask for a hip dysplasia score if you're getting a golden lab.