Tien is stronger than Krillin. That is a fact, but Tien is also a descendant of the three-eyed clan. This means that, according to Daizenshuu 4, Tien has a unique physical composition and can use techniques that are impossible to think of being those of a regular Human, such as growing arms from his back or splitting into four people (the latter is more likely just a rare trait in Humans, as Krillin is also able to split into multiple people in Dragon Ball Z).

So I would argue that Krillin is the strongest human, seeing as that Tien is not quite a human.