Oh my gosh there are so many pros and cons to each age group it is impossible to pick one! When they are infants/toddlers, although you need full time day care you don't have to deal with after school activities. School age kids have vacations that are usually so inconvenient it is so difficult to plan around them for your work schedule. Infants/toddlers need constant attention and care so you have to be very particular about their care takers. Not to mention the expense!
We are lucky that my school age daughter takes the bus to and from school so her dad can stay home with our 13 month old son (he works from home) and just meet her here when she gets home. Our difficulty right now is planning her after school actvities since we share 1 car which I use for work and I don't get home until after 6:30 PM!!