Smaller pups are always confident because they learn to compete with the larger siblings from the beginning. Consequently, small pups are full of enquiry, personality and they are wonderfully trainable. They have learnt to problem solve from day 1 in the face of big bruisers pushing them around. Assuming that a litter is healthy & strong, I have never seen an inferior small Labrador pup. Size is completely 'relative' to the average weight / size of the pups in any given litter. And it is not uncommon for the smallest in one litter to be the equal weight of largest in another litter. And, of course, in some litters the pups are very similar in weight and size. In other litters, there is a greater weight / size range. Small pups / dogs, and particularly males are much more suitable for families with children under 12 and for older people. Larger Labradors can be like run away trucks, particularly if they are not 'puppy pre-schooled' & 'obedience trained'. Don't forget that Labradors are 'retrievers / working dogs'. There is no better breed for a family pet however they must be socialised and obedience trained.
All the best with you selections.