Goku
Vegeta
Gohan
Future Trunks

Goku hands down, While Vegeta is my favourite character there is no doubt that at the end of Z Goku would beat all of them. It's because of motivation and way of training that Goku surpasses Vegeta.

I would still say Goku give or take GT, being the strongest, even though it is stated that Mystical Gohan is possibly stronger than super sayian 3, or at least it is hinted at anyways, but until there is closure on the age old question regarding whether or not Gohan in Mystic form is stronger than super sayian 3 Goku we will have to wait and see, but at least for now I will say Goku. 

I'd say Gohan honestly, while Goku is a genius fighter his son easily has more natural potential simply because he was faced with harder challenges than Goku as a kid, I mean put simply if it were Kid Gohan vs Kid Goku there wouldn't even be a challenge for Gohan (Gohan means rice by the way, and Goku is soup.)

Even in the later story (Excluding GT) it's hinted that Ultimate/ Mystic Gohan could match Goku's Super Saiyan 3 form, not to mention there is no strain on his energy/ body while SSJ3 is tremendously taxing on Goku leaving him completely exhausted after a short period of time, so Gohan could probably outlast Goku physically.

However while Gohan seems to have the more powerful intellect it's more so in an academic sense than Goku. While Gohan is in no way a stupid fighter, Goku is considered a true genius at fighting by much of the cast, and quite frankly it seems to show often as well, so I feel that Goku has the tactical advantage.

As for Future Trunks and Vegeta, well, Vegeta has been proven the inferior fighter compared to Goku, and seeing as I consider Gohan the dominant fighter it should be no surprise that I consider him irrelevant in this topic, as for F. Trunks, well, I mean he was never all that strong, don't get me wrong, at his prime he was among the best, but he was never the top fighter. (*cough* SSJ2 T. Gohan *cough*) I mean I'd (Barely) place him under Vegeta assuming we're talking about Cell Saga, so he's additionally irrelevant.

However versus threads aren't allowed, so I'm going to have to close this, however I figured I might as well share my opinions on the matter.

Thread closed.