My favorite would be "Wanna". The song is what got me into liking Kara (heard it in my friend's car) and after watch the MV of it, I became a devoted fan. I also notice that "Wanna" is the only MV that acually has a story to it out of all (that I've seen) of Kara's MV. The cute parrot was a bonus too!! .......kaaaaarrrrrrra!
Second is "Rock U". Wasn't really into it before but then after hearing it and watching it a couple of times again, it grew on me. Recently saw a a video of Epik high singing that song, cracked me up