I've voted for Pokémon Iris: It's got very good tiles and, Koder has done very good events. I remember that, when this hack was posted, without Koder (the creator was called "Lucky"), this hack weren't anything about what it's today.
But, Koder should have made this hack in English, or at least a translation. I can speak Spanish, but I don't like hacks in spanish. But anyway, it seems very good.
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Azure Horizons: It wasn't as good as Pokémon Iris - It's got Firered and Emerald tiles, and there is only new events/maps. It should be more "customized".
Pokémon Legend of Fenju: If it's base were Emerald/Ruby, I'd have voted for it. But, anyway, it seems very good. But, Pokémon Iris was better.