I think this question is too complex to answer generically.
I would like to make the point, though, that when you're comparing a child being adoped by a single parent vs. living in a group home, in this country you'd likely be talking about a child who is difficult for the agencies to place. Perhaps they're older or have serious medical problems.
Given the OP's motivations including care in old age, I don't think "high need" is the sort of adoption he has in mind.