Time to clear things up since DBZ has enough plotholes of its own. |P
Anyway, based on the vagueness of the question, I'll just address all of the possible answers.
There are two timelines we need to take into consideration, the present one involving teen Gohan, baby Trunks and future Trunks and then future Trunk's...well, future. The first (based during the Cell saga) has teen Gohan becoming SSJ2 and being the strongest Z Fighter at that point in the timeline and continues to be so until the beginning of the Majin Buu saga.
Then there's future Trunk's timeline where he returns to the future to defeat the androids and Cell of his world. Since future Gohan died despite being stronger than future Trunks pre-Cell Saga, Trunks surpasses him and easily dispatches the androids and Cell after returning.
Thus, future Trunks is stronger than Gohan and present Gohan is stronger than present Trunks.
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