I have 2.3eth and I would like to ask if i should hold my eth or buy 21 NEO. I also have ADA|BTC|XLM should I invest more in those also or just go for one full investment
I think you should only invest in altcoins you know the most about it. Don't invest in the opinion of others, it will be very easy for you to lose money because you don't understand altcoin's strengths.
You should keep ETH, it is a great altcoin and NEO cannot compare to it. Soon there will be hard-fork events and it will determine the future of ETH.