For me, it depends on what perspective we're talking about. If it's Ash's story, then DP was leagues better than AG. It really does highlight how much a direct, long-term rival can make a story more engaging, as Ash had no long-term rivals in AG whatsoever. But DP brought Paul, later Barry, and a number of smaller-scale rivals, and suddenly Ash got a lot more interesting both storywise and characterwise, and I think his Pokemon for the most part had a great benefit in the development as well as many of them had their own individual, unique rivalries with Paul's Pokemon.
On the other hand, there's the Contest side of the story. Even though there were BS wins galore in AG, I think overall May's story was superior to Dawn's. Really, the deciding factor there is in the rivals. Drew and Harley trumps pretty much all of Dawn's, both long-term and minor-scale. There's that, and May's starter - while lacking in personality - was so much less annoying and not shoehorned into EVERYTHING the way Dawn's Piplup was. Plus, even though we didn't get to enjoy it for very long, May's starter got to evolve all the way through. I can't imagine May's quest having the same symbolic holding of coming a long way from where she started if she just kept her Torchic the way it was throughout the entire series. But that's another point: May had more dynamic character development that stretched across the entire series, whereas while Dawn did have character development, it didn't feel quite as drastic, and by the series' midpoint Dawn herself barely changed, if at all. While I don't necessarily have a problem with Dawn, her story made me very apathetic about halfway into it when I realized she'd be stuck with dull rivals and Piplup would usurp any development potential from the rest of her team. While not perfect, I think May's team overall had a bit more of a balance in screentime (maybe less so by BF when she got two Kanto starters to pimp FRLG) and I can't recall any of May's Pokemon particularly annoying me. Plus, most of May's one-shot rivals were interesting in their own right. I think Dawn had maybe one or two of those, one I know at least was decent, but still nothing compared to May's. Rival-wise, May's trumped Dawn's in almost every sense outside of Zoey actually winning a GF. And that in of itself bugged me that Sinnoh's GF was totally littered with newbies from the quarterfinals all the way to the finals.
So, yeah. It really depends on who we're talking about here. For Ash, DP is better. For the female Coordintors, AG was superior overall.