(In doing research for this, I have also discovered ICON, but it didn't make the picture.)
I've heard more than once now that if you own Ethereum that you shouldn't buy or invest in Cardano. Sooo does that mean I shouldn't buy or invest in other platforms that are trying to accomplish similar projects. The theory is that if you think Ethereum will succeed then there will be no need for any others. This makes sense because if you look at the car industry, once Ford became successful at making cars, there has never been another car producer. Like Apple and the iPhone, cable news networks, ice cream producers, grocery stores, and I can go on and on.....
Obviously I'm being sarcastic and there are tons of choices out there for all the things I mentioned above. Competition is a great part of business, it keeps people trying to produce the best. So why shouldn't this be the same for smart contract platforms and the other services they provide. There is a ton of reasons I might choose Neo vs. Ethereum. It could be cheaper or maybe it caters more to the project I am working on. Maybe I want to try EOS because its supposedly faster, or maybe I'm Chinese so I like Neo more. Neo has been called the Ethereum of China, I know cryptos are supposed to be international and border-less. People might favor platforms in their region for many reasons. For example, Japanese investors favor Cardano and ICON is supposedly favored by Koreans.
Now I'm not saying that all these platforms will be around forever. In the end the one that can perform the best will be the one that will be worth the most in the future. I have even heard that Bitcoin will be able to run smart contracts, however I will not be selling any of my Ethereum soon.....
Just wanted to throw these thoughts out there. I know I have missed some other smart contract platforms, but when talking of "Ethereum Killers" these four are usually brought up the most.