I hate them both. Gnar has the same issues Nidalee has now. Builds AD but has an ability that deals % max health magic damage. Can't escape him because of Hyper, and Hop. His transformation giving him free health makes it hard to actually poke him out of lane because let's be honest. What champ is going to try and go toe to toe against Mega Gnar early game? And if they do he has the CC and an escape to make it a waste of effort, assuming he does not chain CC you, and kill you. He is ranged, and has ranged poke outside of his autos which slow you, making it harder to actually escape. He is a ball of stats and if you misjudge your ability to win a fight with him, there is no escaping. Honestly if you don't like one, it is impossible for you to not have an issue with the other unless you're just ignorant.
The majority of Gnar's damage can be avoided with side stepping and waiting out his mega form. If you can dodge his Q and can recognize when it is safe and not safe to farm you can beat him with literally any bruiser.
Nidalee however is a ranged melee hybrid assassin split pusher with escapes, gap closers, and heals.
My point right here. Everything this person listed that Nidalee has, Gnar also has, and does. Albeit the heal is more frequent on Nidalee, Gnar still has one. Can't sidestep Hyper, 3 autos and you get chunked, and all he has to do is use Hop to gapclose while transforming. No escaping the AoE CC provided the Gnar is not bad.