Should Mika be a part of one of the assassins that were told to kill the Phantom Troupe?

Or should she go with Gon and Killua to shadow Machi and Nobunaga?

Positive with Gon and Killua

She'll see Machi and Feitan + the other Phantom Troupe members sooner face to face

She'll be with Gon, Killua and Leorio with the arm wrestling

Positives with Kurapika

She'll meet Zeno and Silva (Positive and Negative though)

She'll be at the Auction with Kurapika and the other assassins