What I say is not meant for you, this is what I would do.

If I am in my 30s, how will I be sure that I will never have kids of my own in future? I cannot be sure. Unless there is a medical problem (with me if I were single or with either of us if I were not single). My sister's friend adopted 3 months ago after years of unsuccessful fertility treatment, but she is pregnant now! Her father, who himself is a gyno doctor says that when people are more happy and stress free, there is a higher chance of conception.Ok, I digressed too much.
However good natured we are, there is a biological reality that we must accept. Any mother would show much more affection and care for her biological child, compared to a adopted one. It may not be immedietely preceivable, but subconsciously acting on their decisions. This will create a lot of problems. The point I am trying to drive at is that I will consider adoption ONLY if I am sure that I will not have my own children in future.

IF we discount the above mentioned factor, I would adopt a small baby. But not any arbitrary baby from an orphange. First I would try all my immediete sources. That is, I would ask all my blood relatives if any of them are willing to let me adopt their child. I might possibly be able to offer the child a better living than my relative.They might agree. If that does not work out, then a child of my own race and country(please don't brand me a racist already, there is a logic). Why would I do that? There would be too much social discrimination when it becomes very obvious that a child is adopted. I will have no chance to delay the process of breaking the fact to the child if I go ahead and adopt an african child! Simple logic.
Humans are governed by their genes and environment. When I adopt, the genes are already decided. I cannot change that. But I atleast want some reasonable control over the environment(i.e. nurture). So a small baby is ideal for adoption.