User blog comment:First comes rock/The strongest of the protagonists/@comment-4828844-20131023110550

In terms of physical strength, hand to hand combat, etc., I'll go:

1. Killua

2. Gon

3. Kurapika

4. Leorio (Well, Leorio's been improving lately)

As for Nen:

1. Kurapika or Gon (Kurapika still has his index chain and Gon has his adult form)

2. Killua or Leorio (Killua's Nen ability is pretty common to me though; looking forward for Leorio's ability)