AD&D makes things more complex by introducing nine alignments. Still, the "Good vs. Evil" axis seems more relevant than the Law vs. Chaos one; the difference between, say, Saintly and Beatific or between Devilish and Demonic (which would be nearly synonyms in some dictionaries...) is not as significant as the difference between Saintly and Devilish or Beatific and Demonic.
In addition, rangers must always be good, and paladins not only must be Lawful Good but also cannot associate with non-Good people, although they can freely associate with non-lawful.
You could see Lawful Good as the "best" alignment, in the sense of "summum bonum", while Chaotic Evil are obviously the bad guys.
Once you start looking into the history of philosophy (and religion—although this post is NOT a comment on real-world religions, but on D&D), you begin to notice a certain pattern.
We have a concept of "Good" and certain laws that are meant to help us achieve that good; this is Lawful Good. Over time, the laws—perhaps because they are simpler, easier, or more explicit than Good itself—start to become more important than Good. In other words, the letter of the law becomes more important than the spirit of the law. So Lawful Good begins to slide toward Lawful Neutral or even Lawful Evil.
Then a new doctrine or figure appears. In a way, it is Lawful Good because it offers a better path (a better law) to achieve Good. It denounces the current regime as Lawful Neutral or Evil, and is often considered Chaotic by the existing doctrine, as it appears to defy the letter of the law.
If the new doctrine succeeds, a new and improved Lawful Good becomes the norm—but it is always at risk of sliding back toward Neutral or Evil, as pure Good is elusive for mere mortals.
This seems especially evident in Taoism, Christianity (particularly in its critique of Phariseeism), Protestantism, and Buddhism, but it’s also present in other philosophies. For example, Confucianism is very heavy on obedience and ritual, but Confucius also emphasizes sincerity in performing such rituals.
 

