For long term: $DOT, $LINK $KAVA, $SXP, $EGLD
For mid term: $CKB $CELR, $TROY

IMO, if you want to invest in Altcoins you can see any coins on Binance. You have to find any information about the project you choose, if their project has many good news you can invest there. You also have to see ATH of the project, whether they have made new ATH or not. I don't recommend investing in this bullrun, because no one knows when the bearish will start.