To me, Labs and Goldens have really, really similar personalities. I guess Labs do tend to be more active and oral as far as chewing goes, so maybe those are the types of behavioral problems you are referring to? I wouldn't rule out labs and lab mixes though. They are wonderful family dogs. I grew up with one as my first dog.

I think Collies are great dogs too. Basically, it boils down to individual personalities and the way the dogs were brought up. I'd just visit with as many dogs as possible and talk to the shelter workers to get as much background as possible on each dog.

If you're looking at dogs in the 4-6 month age range, they are still in their socialization window where you could pretty quickly help them out of problem behaviors/habits/fears/etc if they have any. I trained Lolly through a lot of problems at the age of 5 though, so it is possible any time. I wouldn't get hung up on trying to find a "perfect" dog from anywhere because no matter what, any dog will require at least a little training.

I'm sure you know all that. I'm just rambling Good luck!