Depends on your risk level. The higher you can afford losses the more NEO shall go in your portfolio.
ETH is well established, running blockchain and usable.
NEO is mostly speculation but developing and had its first ICOs and NEO is more vulnerable than ETH in terms of Asia news. ETHs price doesnt fall as much as NEOs price during dips. Sure, this can change but thats what recent data show.
Since I am investing in cryptos I made a x8 gain with ETH and a x25 with NEO. I never thought about selling Ether but about selling NEO I am thinking mostly always when the price rises.
If I would decide today, I would buy 9 NEO and about 0,8 ETH.