That title belongs to all of those multiplayer Zelda games, they're really mediocre imo.
The worst thing about Phantom Hourglass is the stressful tedium that is the Temple of the Ocean King, but outside of that terribleness PH is a really fun little action adventure game that manages to translate Zelda's gameplay to a touchscreen/dual screen setup in a surprisingly elegant and sometimes brilliant way. It ain't my fav, but it's still good. Oh And Linebeck is an awesome character.
Spirit Tracks on the other hand is the business, fuck the haters, that game's an underrated gem (Minish Cap > Spirit Tracks and its train >>>> all your fav top down Zeldas, don't @ me. Hit ignore, you'll feel better). One of the DS' best imo.
The game uses PH as a base and improves on it substantially (The Tower of Spirits is one of the best Zelda dungeons with one of the most compelling features, Phantom Zelda) while also feeling like the unique non-(old)Hyrulean follow up that Wind Waker was asking for.
It had a small but fun and unique selection of items.
The cutscene direction is surprisingly sophisticated and the storytelling is wonderful.
It plays with the established lore in fun ways while also providing its own unique worldbuilding elements.
It's version of Zelda is one of, if not the most charming and well developed in the whole series.
Chancellor Cole and Byrne (especially) are really cool one-off villains.
And the music is absolutely amazing, can't get enough of that overworld theme.
It's honestly one of the few handheld games that I wish was made for a home console instead. The only thing I genuinely dislike about it is that damn flute, those mic controls are wonky af. But that ain't enough to spoil the game for me.