difficult question
i love almost all their songs. i would say that it's easier for me to say which song is not that good (in my opinion)
i really like Sungkyus solo songs. especially '41 days', 'because' and '60 seconds (the band version is also very good). sungkyus angelic voice is so adorable XD
i also like the songs 'special girl' and 'without you' from INFINITE H
but the songs that i can't get enough from since their release are nothing's over, btd, can you smile, last summer, i like you, be mine (remix version), she's back, inconvenient truth, white confession, man in love, the chaser aaaand destiny
its alot i know but infinite is my ultimate bias