Which ult is stronger, AD Gangplank or AP Gangplank?

I think AP Gankplank benefits more from upgrading his ult, but what is funny is, the barrels he uses to farm his ult faster, only scales from ad. If I was a GP main, I would not even bother to waste my time using my q to farm my ult, I would use it to simply poke my opponent as the ult does not really benefit ad GP. And AP GP, who really benefits, can't farm his ult as fast. Its also funny the barrels work with trinity force active spellblade, but it does not for lichbane.

Let me know your thoughts....