Famitsu, the most popular gaming magazine in Japan, is notorious for their uncompromising and strictly regulated review system. Indeed, only six games in their history have ever received a perfect 40/40 review score.
Since their opinion is highly valued, a couple people over at GoNintendo have compiled a comprehensive list of the top-scoring DS games on the market. First place belongs solely to Nintendogs, picking up one of those coveted 40/40 scores, followed by Meteos with a 38/40, and then Animal Crossing: Wild World at 37/40. For a (very) full list, click that underlined blue clicky thing at the bottom of the post.
(If you were wondering, the six perfect scores belong to (in chronological order): The Legend of Zelda: Ocarina of Time, Vagrant Story, Soul Calibur, The Legend of Zelda: Wind Waker, Nintendogs, and Final Fantasy XII.)