My favourite trading sequence was probably that of Phantom Hourglass. You had no idea what the hell you were going to get, and you had to figure out who to give each item to for yourself. Virtually no help was given. I really like that, it posed a challenge. Also, I really liked what you got. It was kindof useless, just the great spin attack, but I really liked the way it was portrayed. The fact that this 'wayfarer' had found some rare legendary swordsman's scroll. I'm sorry, but that's just cool.
I really didn't like the on in LA. I didn't like the way it was done, the fact that all you needed to do was just walk around and something would eventually reveal itself to you. Also, I didn't like that it tied in with the storyline. I like a trading sequence to be a side-quest, that gives you something that helps out, but isn't required in the game. I know the boomerang wasn't required, but I heard that without the magnifying glass, you can't see the book in the library which tells you the way through the wind fish's egg. Also, I don't like the fact that you go through the whole trading sequence, then when you get to the end you have to trade one of your own weapons to get the boomerang. That just annoyed me.
However, inspite of all this, I think the boomerang in LA was the best item to get in a trading sequence. It was really worth the effort. It killed most enemies in one hit, and personally, IT WAS THE BOOMERANG! I had to get it because it's in like almost every Zelda game. The shovel is useless anyway. I liked the boomerang and I used it alot. This was one of the things I really liked about this game, the fact that the boomerang, an item that I usually never used, and normally was instantly outstripped by the Bow and Arrow actually had a purpose. I liked that alot.