Are you keeping them on the exchanges or downloading a wallet for each altcoin you buy? is there a multi wallet that has support for many altcoins?
For long term, i use paper wallet. For short term, exchange or my computer wallet. I would like to buy Nano S in near future. I don't store it longer on non trusted exchange.Binance, bitfinex, bittrex and coinbase is where i store most of my cryptos. I feel safe with them.