According to Enterbrain, Dragon Quest VI: Realms of Reverie sold 909,981 units in its first week and that makes it the top selling Dragon Quest remake on the Nintendo DS.
Media Create data notes Dragon Quest IV: Chapters of the Chosen sold 597,000 copies its first week and fan-favorite Dragon Quest V: Hand of the Heavenly Bride moved 644,000 copies. While these numbers are from a different source, Dragon Quest VI is clearly outpacing the other games in the Zenithia trilogy.
Perhaps, this is because this Dragon Quest VI remake is the only Dragon Quest VI remake. Dragon Quest V was re-released on the PlayStation 2 and Dragon Quest IV is also available on the PsOne.