I'd say SIN. Why? Very simple, an average SIN player VS any other class (including destroyer), will try the combo that removes 50% of your life... then repeat. If it doesn't work, he will play full invisible and win with time. This works against all,. I'm not a SIN hater, just that overall SIN played in average is most OP.
KFM, hummm i can only say KFM bot = summoner bot, they can't be defeated (or really really hardly). If a human could have those timings (some do, but do you consider pro chinese players human?...), KFM and summoner most OP. So yeah if your really good with KFM, t