There has not been a better handheld Zelda game then Links Awakening. That game is still one of the best games ever made for any handheld or console and absolutely pushed the limits of the Gameboy. The game looked almost as good as a SNES game on a snot color screen. Phantom hourglass looks great but it doesn't push the DS the same way that Links Awakening did.
Links Awakening is easily in my top 20 games of all time.
Since I've played all of the hand held Zeldas (I exclude LTTP based on it's port from the SNES status) here is a list of how all the games rank and score I'd give them.
1. Links Awakening 10, this game deserves it's perfect status
2. Minish Cap 9.7, if the game had been a bit longer it would have scored higher. I also deducted marks for it not having a very even dificulty. Most of the game is pretty easy until you get to the very end where they beat you with an ugly stick of hardness.
3. Phantom Hourglass 9.4, I'd score this game higher if they hadn't reused the same level over and over (worst idea ever for a zelda game). It really ruins the replayability of the game and makes the game harder due to frustration with the level design.
4. Oracle of Seasons 9.1, The game was a lot of fun but it felt too much like a me too rather then something completely new. They reused Links Awakenings graphicsbut forgot the heart and love that L.A. has. Still great and a must play though.
5. Oracle of Ages 9.0, Want one of the hardest Zelda's ever made? These puzzle's drove me nuts, sometimes in a good way and sometimes not so great. I suck at rythem games so I had a hard time with one of the early puzzles ;) still a great game though.
Prepare for termination! It is the only logical thing to do, for I am only loyal to Megatron.