There are lots of altcoins(well, ICOs) Can anyone suggest some altcoins to buy?
I searched some on ICO listing cites, but it seems a lot of them are paid to be rated high. Some coins have only 100+ members on Telegram...

I know that the price will go up and down but how to find some altcoins that is really doing something revolutionary and worth to invest?
That's why it's very risky and really not recommended for me for investing in any ICOs today. Try to some altcoins/ tokens that are already listed way back 2017. You can try to read here
https://bl4nkcode.info/crypto/article/top-5-most-promising-coins-to-invest-in-for-2018/ if the coins listed is much worth investing, just make sure you research well by reading different articles before investing in any means.
Yeah I agree. Research is the key to find some good projects, coin and tokens on the market nowadays. But if OP wants to have a much safer investments I highly recommend coins that are already listed on exchanges and listed top 20. My previous investments are poured into Litecoin, Ethereum, Dash, SXDT, IOSToken and now I currently enrolled in a bounty campaign program that for me has potential as they have already proven the effectiveness, creativeness and usefullness of their application though they are mostly heard in Asian countries and that is no other than SWIPE.