First off, good luck for you talent show this year.
Second, I would recommend History or Mama, neither are difficult or complex, just a little bit fast and looks very impressive when done well.
Face by Nu'est is probably good choice as well, it's fast and probably a little complex - especially the foot work - to learn.
If you do break dancing at all, you could do Zinni's parts in I Like That and modify bits of it from the MV into the actual dance.
You could also do the dance that the SEVENTEEN maknae line did to David Guetta's Titanium.
Warrior or Oneshot by BAP seem to both be fairly difficult, though I haven't actually attempted either.
You Know Me and MAMAMA by TASTY both probably have difficult dances. I'm not a hip-hop dancer so I'm not familiar with the moves so all the dances are difficult to me, so I wouldn't know, but they seem pretty hard.
Tarantallegra and Incredible by Xia Junsu are both difficult too, I've actually attempted them and to be honest, I gave up one them quickly and probably won't get back to them for a while.
Finally, Y by MBLAQ is probably also a difficult dance, since the choreographer is notorious for choreographing stupidly difficult dances.
I hope these will be helpful for you, I've purposely left out INFINITE since I'm not particularly sure which ones you've done, and SHINee, since you've already done a few. Though have you considered doing the ones you've already learnt for the talent show.