For me:
Hands Up - MEOVV was actually so hard lmao I almost gave up
Jellyous - ILLIT everyone scarred me saying it was so hard but it wasn’t that bad it’s just a lot to remember
I thought chk chk boom would be a hard dance but it rly isn't, also magnetic, the hand movements are a bit confusing but if you look at it slowly, its rly easy to learn
the hardest dance i learned was probably 'stay tonight' by chungha, and or 'im ready' also by chungha!
the easiest one was maybe 'jellyous' - illit and '1&only' - xlov!!
but there are A BUNCH of choreos ive learned so honestly i dont rlly remember but these are the ones that seemed like the best