For me, the best competitors of ethereum, are RIPPLE and STELLAR. As you can see this two cryptocurrency very near on the top and ripple takes the number two spot. Which is ethereum place. Right? And stellar also near to ethereum. So i think this two are the best.
Ripple can compete with Ethereum only when we mean the market capitalization. When we speak about the future of these currencies, for me, ETH is in the first place. NEO can compete with it in future.