Defiantly the whole frieza arc... like Merle said goku going from 180,000 to 3,000,000... and depending on the levels u use the whole SSJ and frieza levels. Like if people have frieza actually at 1% and 50% being 70,000,000 and max 150,000,000 is super hacks. even if u use low numbers goku going from 180,000 to 3,000,000 for no reason is wack
piccolo going above frieza and goku is easily possible using low numbers. like 2 million to 20 million is more believeable and actually possible compared to 2 million to 200 million+ with high numbers.
with cell its really the same. using small numbers it makes complete sense. for example NYC is 8 million people. on average their power levels is 5 so if cell absorbed NYC thats 40 million. now in the show cell got smaller cities and towns, i have him going from 18 million to 35 million. so thats a 17 mill increase meaning he aborbed about over 3 million people which is completely possible. while high numbers he increases like 300 million, which would mean he needed to absorb like 75 million people! which is like 1/3rd of the USA which is definatly not the case lol. so again depends on the numbers you use it could either make complete sense or no sense
some ones i see are the humans getting stronger than raditz training with only kami and popo for 1 year. logically they should be the same level as goku or less. theyre getting the same training from the same people but only 2 years less of it lol. doesnt make sense.
gohan goung from a scrub who didnt know ssj to all of a sudden passing goku" in 1 years worth of training (i beliueve he wasnt stronger than goku)
i'll add more later. sorry for the spelling my computer is really laggy. i'll add more when the lag stops