Seyong is the definitely the best dancer in MYNAME. He has talent in street dancing, and frequently does handstands (in Message) and has solos in live performances.
Insoo is the second top contender for best dancer. He used to do ballet and was teaching some famous people before joining MYNAME. There was also a TV episode where they counted how many pirouettes he could do.
To compare them two, there is a video of their different dancing styles to Hello Again.