I could say Gehaktbal or P1naattike1tto but I haven't really played much against them (Geha I havent seen around in a while, and P1na always turns me down when he finds me in ranked matches), altough I could clearly see Geha was bloody dangerous. Annoyingly dangerous.
I'm gonna go with another 3 people:
1) Regick (one of the best DoAU players, one of the best DoA4 players. In DoA5 he's not as strong as he used to be but he's still a strong player. I hate his style... it's the opposite of mine, we're really uncompatible but I can't deny his strength)
2) PowerInstinct(x360)/WindFireEarth(PS3) - (he too is possibly not as good as he used to be, but he's still very dangerous. I love his Lisa and Lei Fang, his style, the fact he's always coolheaded, calm and never arrogant or disrespectful towards his opponents)
3) Powerking87 (nuff said! Love his Christie but all his characters really. What I mostly love about him is that he tries to play with style and coolness rather than aiming just for a cold and not-fun victory. It's incredibly fun to play against him)