WAAAA YES I CAN DO THIS.
Personally, I think the best way to go about it is to just go backwards in their discography, because their songs have been getting better and better.
I think their two best songs are their two latest singles.
http://www.youtube.com/watch?v=H4dO_-Cj-Ss <— Tick Tack (Their first Japanese single)
http://www.youtube.com/watch?v=n3dF0Y7deb0 <— Neverland (their last promoted Korean song)
http://youtu.be/h1zOhQQpw6U <— 0330, a ballad. It a great song, and I think this song was such a game changer. XD U-Kiss didn’t do ballads before, but they did a member change and leveled up. (It’s not the type of song I listen to on repeat forever like I do with some of their other songs though. The video story is also kinda really dumb…)
These three have the current 7 members: Soohyun, Kiseop, Eli, AJm Hoon, Kevin and Dongho.
http://youtu.be/Iiikpj15i84 <— This is 시끄러!! (Shut up!) which has the previous lineup, Soohyun, Kiseop, Eli, Kevin, Dongho, Kibum and Xander. Kibum and Xander were replaced by Hoon and AJ about this time last year.