I believe the best fishing in Maui is April-July, which is obviously not when most people are there. I was there in June last year and did a shared charter out of Lahaina with a boat called “die hard” they leave earlier and go farther out to the bouys than the other charters. The bouys are generally where you will get the mahi and tuna. You then troll back in for the bigger fish. We caught yellowfin, skipjack, and mahi at the bouy and then got one nice wahoo on the way back in and lost another.
I would ride down to the marina every day and check catches and die hard was definitely consistently the best, and even though weather conditions seem the same everyday, even their catch rate was highly variable day to day. They did usually get tuna and or mahi every day but numbers and size varied. I did see them also get wahoo, marlin, short billed spearfish . Most boats don’t get out to the bouys so they are just trolling for the big fish around Lahaina which can just turn into a boat ride, and you likely won’t get any mahi or tuna. The best part was the gallon sized ziplock bag of fish I got that I grilled the rest of the trip, freaking amazing.
You can research charters on yelp, trip adviser etc to make your choice. Die hard isn’t for the faint of heart because they get out in rougher water, so dont think you are too tough to take something for sea sickness. The two guys on my boat that thought they were tough were both chumming ��. Hawaiian waters are no joke and it was rough, and our capt said that was about average. He said rarely do they have a charter that nobody chums.