Crypto market is go down in this movement. I have some USDTs. So I want buy some coins. Is this time good for buy? What are the good coins to buy and Hole long term? Any suggestions? 
For me the good ones are the top coins in the market which you can hold for a long time without being scared of them dying out before they can get to a good price and make you a good amount of profit. Buy ethereum, buy bitcoin and buy other altcoins like litecoins. The bigger the better and the more investors they have the less likely they are to fail.