i'll choose (a) but depends on 老公是否也好忙. better if either one of you can spend some quality time with the kid during weekday esp the time before the kid goes to bed.
i'll also choose (a) if it's a five day job. then i'll make sure that my kid enjoys the weekends with us parents.
i'll also choose (a) if the kid can be trained to be more independent e.g. can do homework and study by himself/ herself.
i'll choose (b) if the kid's health is not good and often needs to see a doctor. that means he/ she needs more parental care (physcially and mentally).