To me, the following are better in OS than other sagas:
Characters that didn't wear out their welcome.
COTDs that were actually compelling instead of just stock characters (mostly Kanto)
More creative stories that aren't just copy and paste from the games
A more grand sense of adventure
Better battles that weren't drawn out, nor did they try too hard to be "epic", which they're not (that last part is not referring to OS battles, in case some people are confused).
Marketing didn't get in the way of putting out a good quality product crafted with effort and passion.
Aimed at a wider age range, which meant there was something for everyone.
Actual emotion that wasn't forced (both characters and stories).
Best character interactions.
More iconic Pokemon, as well as better personalities for them (well, most of them).