Depends. Lure is the best choice if you don't plan on taking Drop. Otherwise, since Drop is difficult to level, you may want to get it as soon as possible. I mean, I took drop as my
last gag, and I'm still struggling with trying to level it.
Low-level Lures, on the other hand, are useful in just about any battle. Even a $1 can help out occasionally against the big cogs, and the small magnet as well.
Best to decide now which of the gags you DON'T want, since you're not getting one of them, whether it's Sound, Lure, Drop, or Trap.