Kids will always be different, some get along better than others, despite ages. But its a fact that most teenagers don't want to hang out with their 7-9 yr old siblings. Which leaves the younger one feeling left out and alone, unless there is another sibling after them.
We had our first two close together. I wanted more, but with working, time got away from me. I couldn't ignore the pangs of wanting another baby and decided if I wanted another it was now or never...I was 30. Now my first 2 are close to being out of school, while my youngest is still in elementary school. I wish I would have thought about all that when I was wanting that baby. I will be almost 50 when the 3rd graduates high school. My teenagers act like DH and I are old now and we are only 38....I can't imagine how my son will feel when his 48 yr old parents are taking him places. Some days when the older two are hanging out at the mall with friends, I feel like my 8 yr old is an only child. I wish I had the nerve to have a 4th, but I was scared to tempt fate and so DH got fixed. I don't regret having my 3rd, he is a real treasure, I just feel sorry for him sometimes.
The choice definitely has to be yours and your partners. You have to decide the time you want in between kids, how many you really want, how badly you want them as opposed to the degree, can you get help with the baby while taking classes, would you be happy with just an only child if work later on doesnt allow for another baby...I applaud you for doing the school/career thing, its tough.
A career will make you money, if you are lucky, and status...a child gives you love, memories, and carries on your family. It all comes down to what is most important to you. Good luck with your decision!