A big problem with COSS right now is that they are not getting any coins anyone wants to trade. If you look at COSS trading volume it is mostly just their own token being traded for volume.
For KuCoin they have onboarded many new altcoins such as Bounty0x, DeepBrain Chain, Oyster Protocol, and Red Pulse. All which have pretty high volume on their exchange.
One thing that can make COSS better is that they plan to make it a fiat gateway. If they succeed in that then they will generate exponential growth in my opinion.
I hold a bit of COSS in case they do succeed in the fiat gateway, but for now more of my holdings are in KCS than COSS.
Referral link for Kucoin: https://www.kucoin.com/#/signup?r=E5i24V
COSS seems more steady from an investor perspective but the project is much smaller and less developed right now than KuCoin. That means that the biggest growth potential is also with COSS.
Patience will pay off.