
Hi, you're certainly doing your homework, which is marvellous! :) There certainly seems to be a slight difference in temperament between the three colours of labrador, with the chocolates having the reputation of being the slowest to mature. They are also the colour that needs the most research into their background because they are the 'fashionable' colour, and as such many breeders (not all, by any means) have jumped onto the bandwagon to churn out brown puppies regardless of health.
Good chocolates are certainly quite rare - poorer quality ones aren't. They also seem to be commanding the highest prices simply because of this.
I personally prefer the leaner look of the working-bred labrador over the heavier-set show-type, but the working type can be so eager to be 'doing' that they can be too 'hot' for the average pet owner. Gender-wise I prefer the bitches because they seem to be more homeloving and family-orientated, whereas the dogs (at least the ones I know) seem to be more boisterous and independent, while still being very loving.
Price-wise, the thing to go for is health. There are several hereditary conditions that labradors can suffer from. Breeders whose stock has been successfully health-checked tend to ask a bit more than the 'pet' breeder down the road. Make sure that both parents have been hip-scored (see the certificates), ideally elbow-scored, and have passed their annual eye-checks. For many of these tests the dogs have to be Kennel Club registered, so don't go for either unregistered pups, or pups with any other registration. The slightly higher cost of a healthy puppy from healthy parents can save you many hundreds, if not thousands, of pounds in vet bills.
Another point to mention is that very many reputable breeders simply don't breed puppies to be ready at Christmastime. You may have to wait until the New Year. But what's a few months when you'll be getting a dog who will hopefully be a loved family member for about 15 years?
Good luck.