We must address the elephant in the room.
The is the perfect curated library. It fits comfortably on a 2GB SD card, boots instantly on any handheld emulator (Anbernic, Miyoo, Retroid), and gives you roughly 3,000 hours of gameplay without a single dud.
: While primarily for original Game Boy/GBC games, it features a visual interface for creating RPGs and platformers that can sometimes be adapted for GBA-style projects.
The GBA library has roughly 1,500 titles globally. Out of those, only about 200 are considered "worth playing" by modern standards. The "Top 165" packs trim the fat even further.
The dust on the cardboard box was thick, but the Sharpie scrawl on the side was still legible: "GBA ROM PACK - 165 TOP."