My experience told me the 2 children shd have 3-3.5yrs distance.
elder one - 3yr - 3.5yr
younger one - new born
Good points:
1. Better relationship, no more jealousy (of course u know how to handle)
2. the elder one go to school, have enough time to take care the younger one
3. for parents, the time for fostering children wld not be too long
more more ....
my personal opinion is the ideal age range between 2 babies be 1-2 yrs and with same gender. of course, it will be a very tough job to take care of two during their early ages. i have 2 sons (1 is 3 yrs and 1 is 1.5 yrs) and they have very good relationship and can learn things together (definitely it will speed up the learning ability of the younger baby).