Three of the load-bearing phenomena of ethics are happiness, obligation, and character. Each of these can be considered in a lot of different ways, but as it happens, in each case most approaches to ethical questions in general fall under one of two possible responses to each.
(1) Happiness: In practice, the key ethical divide on the question of happiness is whether happiness is subjective (S) or objective (O); another way to put the matter is to ask whether the feeling of happiness and actual happiness can come apart. Mill and Aristotle both talk about something that can be characterized as happiness, the fulfilling good of a life, but Mill's account is subjective, characterizing this fulfilling good in terms of pleasures and pains, while Aristotle's account is objective, characterizing it as a totality of good relevant to one's nature.
(2) Obligation: The most significant divide on the question of obligation is between positivists (P), who think that all obligations are made into obligations for us, and naturalists (N), who think that some obligations are not made but natural to us in some way (due to the nature of reason, usually). Thus divine command theorists and natural law theorists are divided by the fact that divine command theorists are positivists and natural law theorists are naturalists.
(3) Character: Dispute about the nature of character is a trickier landscape, but a big division in approaches is the one between those who take the standard of good character to be based on some kind of moral sentiment or feeling (F) or on reason itself in some way (R). Thus Hume and Aquinas both take character to be very important, but Hume is a sentimentalist and Aquinas a rationalist.
These are very different divides, but there is a sort of commonality among the three, since in each case one side makes the idea in question more objective than the other. There are also different ways you could divide ethical approaches that interact with these in important and interesting ways, the most important being the divide among consequentialists, deontologists, and virtue ethicists. An ONR virtue ethicist and an ONR deontologist will have a lot in common, but they will differ as to the kinds of things they think are fundamental. In any case, these other divides can be set aside for now.
We then have a set of families into which we can divide fully developed ethical approaches, that is, ethical approaches that have some kind of substantive account of each of these:
SPF
SPR
SNF
SNR
OPF
OPR
ONF
ONR
Aristotelian approaches to ethics are usually ONR, although occasionally you find modern Aristotle-inspired approaches that are OPR, a position that is suggested by Anscombe's "Modern Moral Philosophy". Kantianism is very explicitly SNR; much of the structure of Kant's overall approach to ethics is that he accepts the empiricist account of happiness, which is subjectivist, and wishes to integrate that with a rationalist account of obligation, which is naturalist. Utilitarians are all S's, although not all consequentialists are, and Mill is a positivist about obligations, so he's at least an SP. It's a bit trickier to say whether he is SPF or SPR; he says things consistent with both. Without a full study, I think the evidence, particularly from the essay "On Bentham" indicates that he is SPF. Hume seems to be SNF -- he's definitely an F, since he thinks character is recognized as good or bad by moral sentiment, and he does not in fact treat all obligations in positivist terms, but traces some of them back to the same moral sentiment, which would make him technically an N. The ethical approaches that tend to say things that sound most like ONF are moral sense theories, although I suspect that they are sometimes really SNF. I'm not sure if there are any OPF approaches, but perhaps some divine command theories come close.
