DS. As much as people love to funk on it for it's gimmicks, there are some absolutely great gaming experiences or additions thanks to those.
Hotel Dusk and it's Sequel, The World Ends With You, Ghost Trick and more exist thanks to DS being a DS
Not only that, thanks to pretty good design, hardware power and additions to controls, DS is also far better with more traditional games than GBA. Games like FF3, FF4 DS, Chrono Trigger DS, The Castlevania games and more.
While GBA is lovely, has in my books "the last great (fun) pokemon games", Boktai and other wild fun stuff, it had very little time of existence, a very small library, and even with all the good games it is like trying to figure out is PS1 or PS3 better than PS2. The numbers just are objectively way too overwhelming to come up with any other results.
And I say this as someone who had both consoles when relevant. With that I could also add that poor kids could eat all they could with DS if you just knew about a certain word and a Chinese website shipping one to your country.