Hi Matian,
I’m assuming you are in the UK, because I understand there is a big difference between UK and US field/working labs regarding temperament.
The difference can usually be understood if one looks at why they are bred. Three things are of paramount importance in a working dog. Ability / intelligence, temperament and health. Looks are secondary. A show lab is bred with regard for the breed standard – so for looks / conformation and temperament.
Working labs have been bred to work in the field all day, They are active, intelligent (so easily trained), and have a natural hunting ability – so need plenty of exercise (when old enough) and lots of mental stimulation. They can be great family dogs in the right active type of environment. But, they can also be destructive if they do not have enough to keep them occupied, both mentally and physically. Their natural intelligence does make them easy to train and they will be bred with temperament and steadiness in mind (a working lab has to remain totally steady regardless of the excitement going on around him). However, they are not born this way, they do need training, left to their own devices, they will very likely train themselves to do things you won’t want them to learn. If you have plenty of time, are around all day and want to spend time training, (not just basic puppy classes) and be involved in activities and can give them plenty of exercise then a lab from working lines is great, otherwise I would tend to go for show lines.
HTH