Killua has more precision, Gon has more endurance. Killua has more strategy and has been tutored on tactics, Gon has more natural insight and guts.
In many ways, they enable each others- a good example would be the fight with Raizor, where Killua was shown having extreme precision when it came to aura reditribution, but gon was shown to have a ever-increasing tempo.
Also, 'amount' of nen comes in different ways. First is obviously the amount of nen in the aura. Second would be the amount of nen that can replace that (reserves), and third would be the amount of nen in a particular area of the body.
I'd say Gon is by far superior in the first two category, BUT Killua is not only far superior in the last one, but he doesn't need much if any 'prep time', or 'motivation' to fight ot his fullest. Gon gets much, much stronger against an actual enemy (Killua actually was the opposite for a while).
As for techniques- Killua had mainly two 'powerups' during the ant arc, if you discount the sheer base stat increase by biscuit's training. The first is taking off the needle, the second is Kanmaru.
Gon mostly improved (beyond base stat increase from biscuit) his jajanken, as well as his understanding on how to use it for the first part, but then improved his 'hated race' trait.
There is no telling how that one works yet.