i say trunks for same reason as everyone else, he just kinda sucks late game without stronger transformations.
goku can steal quests like no other with his solar flare, and he also gets ss4, and can transmission around the map for dragon balls, so goku is very easy.
vegeta has ss4. thats about all he has going for himself.
gohan with his mystic ss2, and saiyaman with power pose is pretty powerful.
gotenks, once you get them high enough level to be able to fight for themselves, send them on seperate paths, so they can creep 2x faster than anyone except androids. then fuse them.
trunks, he has no real late game, but he has really strong start and mid game b/c sword and upgraded sword. but late game, he's got nothing.
piccolo has his fusions, and other than that is in the same boat as trunks. except for the fact that piccolo has better skills and regeneration. so in the end, piccolo > trunks by a lot.
Buu is freaking easy. i don't see how people say he is hardest to use. just level up till you get super buu, and then go straight for Z fighters to absorb.
bebi, is tricky. you gotta be able to play him really well, but in some ways, he is one of the strongest. the main thing that matters is to get a body early. take someones body asap, and when the body is damaged enough to boot you out of it, just hop back in really fast, and it heals the body. power up in a body till level 45, enter bulma's body, turn super bebi, then GOozaru bebi and you're a powerhouse.
cell, if played right, can steal quests just as well as goku can. simply don't absorb 17 or 18. if you don't turn perfect form, you can use windwalk and steal all the quests you want. after you steal some main quests, like raditz's drop, and tree of might seed, absorb the droids and turn perfect.
androids, same plan as gotenks. power them up together untill they can solo, and send them off in different directions. when far away from eachother, they don't have to split exp 3 ways, and each individual gains stats for their own kills, instead of them sort of splitting the stat increase for kills. once they are all level 10, you're in a sort of safe zone, where you know they won't be going to hell, and just creep 3x faster than everyone else except gotenks, and then wait for Z fighters to catch on and kill your droids, fusing them to 13, and then you'll be a storng as hell super 13.
Broly, is easy once he is level 6, he can ressurect after dieing like every 4 minutes. as broly, in a fight, you don't gotta worry about killing the enemy before they kill you, you just gotta get them below half hp before they kill you. broly is early for creeping also, because his damage increase skill, he can kill stuff way faster than most people early game, and if you keep up your creeping pace, you'll stay stronger than most enemies, or at least you'll stay strong enough to kill them more than half way before dieing
geti is the most noob friendly, but in some ways also the least noob friendly. most noob friendly in early game, because you respawn instead of going to hell. least noob friendly late game b/c noobs never know to upgrade their geti star, and build resourcing buildings so a noob geti always gets killed b/c they don't know how to gather resources, upgrade, and make clones.