For me it has to be AmberELEC.
Video previews, the option to view a game guide, and an icon on the games list to indicate a game has Retro Achievements combined with an easy to view list of achievements.
It was fantastic and the reason I’m hesitant to sell my RG351V
The OG CFW is before my time I’m afraid, so it’s hard for me to say what’s changed. It’s pretty utilitarian if I’m honest but I can report it’s super stable.