There is no "chihuahua" breed, & very few places where Chihuahuas are #3.
Ask your ADULT-behaviour neighbours what features they would want in a dog. (Classify as "childish" anyone who places "cute" in their top 5 criteria)
Turn their responses into a table.
I'll bet that the most popular features all fit the 3 breeds you listed.
Way 'up there' will be a version of:
• "Soppiness. All 3 adore their humans, are sensitive to moods, and make GREAT "fur therapists" - for their own household, also as PAT-dogs (Pets As Therapy).
• "Size". All 3 are big enough to be easy to pat. Pups are unlikely to be trodden on before being noticed, yet adults are small enough to pick up & carry to the vehicle and from vehicle to vet when too sick/hurt to walk.
• "Easy to train": Herding and bird-dog breeds were selected for willingness to interpret & take notice of the strange un-dog-like noises & postures humans produce. Of the 3 you list:
-- Labradors are most likely to frustrate owners by being intelligently stubborn when THEY want to do something (in pre-radio-controlled-shock-collar days, we never could solve the district nurse's problem with her Labrador - it behaved perfectly while she held the 50 feet of sash-cord attached to it's leash, but as soon as the cord was dropped the Lab was off for a happy trot around the race-course where we trainedt).
-- GSDs are most likely to frustrate owners by out-witting brainless human intentions (my Ciwa worked out how to put her nose though the hole in the gate for me - and then HER! - to lift its D-ring from in the pen and thus open the gate. I put her in a pen with a sliding bolt. She vibrated the gate until the bolt slid back, allowing her to push the gate open. I chained the post to the gate-frame so the gate couldn't be pushed open enough to let her through. She lifted the OTHER side of the gate until the hinge-rings lifted off hinge-pins.... I then wired a hinge to have no vertical movement - THAT kept her in). They also get bored if required to do the same thing too many times, and love to work things out for themselves - which makes them the best as guide dogs but also the longest to train, because you can't just repeat a command 100 times in a row to "make it sink in". As REAL breeders of GSDs require all breeding stock to have passed all of http://pets.groups.yahoo.com/group/The_GSD_Source/links/Defining_a_GSD_001261993982/
, buyers from THEM can be assured of good character, courage, calmness, and satisfactory joints.
-- GRs are least demanding - not especially intelligent, but dead easy to train, and happy to repeat the same 4 or 5 things all day - which is why time-is-money commercial "trainers" prefer them when asked to supply guide dogs.
• "Low-maintenance": All 3 are meant to have coats that are weatherproof, and dry almost as soon as the dog shakes. Although GSDs & Labs have a reputation for being susceptible to HD, GSDs are down about 40th on OFA's list of "breeds most likely to suffer HD"; Labs about the same. BOTH breeds have clubs that promote NOT breeding unless both parents have passed various tests, with joint certificates being top in both cases.
• "Doesn't drool/slobber" and "Doesn't need lots of vet-care" will probably also be high up. Between the 16 weeks booster and geriatric care at about 11 years, my GSDs see vets for only wounds, hip & elbow xrays, and pre-mating tests.
And all 3 breeds have REAL JOBS, which means that despite the worst efforts of show-exaggeration-is-all "breeders" and puppy-cuteness-is-all greedy BYBers, each has many dedicated breeders who insist that THEIR litters have the full potential to PERFORM the breed's tasks. It's a pity that so many people think that mating just any pair of a breed will produce pups that will possess all the characteristics that breed is noted for, and so pet shops, puppy-mills, and ignorant BYBers thrive, but popular breeds have their reputations degraded.
Les P, ownr of GSD_Friendly: http://pets.groups.yahoo.com/group/GSD_Friendly
"In GSDs" as of 1967