Minish Cap! Oh man, I have only recently gotten to play this game and it was a slice of zelda goodness that challenged even a few of the console games in the fun department. My only wish is that it was longer and that Nintendo would put the handheld side of the series back into Capcom's hands. ;-;
Even though my first slot is a no-brainer my second favorite handheld in the sries is... a much more complicated pick for sure. I think I'll say it's Oracle of Seasons.
Out of the duo, it was the one I really dived into and thought the game had a great flow to it. The "difficulty" factor doesn't really play a big part for me, and in fact, the reason I don't like ages more is because it gets increasingly frustrating later into the game. In my opinion keeps you distracted from progressing in the story a little longer than it should, and I found whenever I turned off the game I would have that OoT water temple moment: "So... where was I?". Never found myself in that sort of situation in Seasons.
Though I haven't played much of LA I plan to play that game all the way through, and from the little bit I've played it's safe to say it might very well top Seasons and nab my second favorite slot. c:
Haven't played much of the DS games to be quite honest (I know, bad bad zelda fan ;-;'' ), but from what I played I don't think they would top Minish Cap.