I want to invest in a coin that is stable.
No such thing! The best thing to do is diversify. Don't buy just one coin. Buy a small amount of 5-10 different tokens.
Just some friendly advice

Sounds like excellent advice to me.
True. You shouldn't put all your money in any single coin or product. You must need to diversify your funds to reduce future risks. You should select a coin based on the use of their coins because there are many coins not useful. I have invested some money in these coins IOTA, NEM, Waves, LTC, Ripple, Burst, ETH and NVO.
Diversify is always the best thing to do when it comes to investment and we should really not focus on a single coin because once it would failed you would really have the hard time to recover compared to have many since if one of those coins failed you do still have coins for you to recover and its much better than to those who havent. I invested most of my coins on cheap coins inside top 20 on coinmarketcap.