You may not choose between Bitcoin and altcoins, but choose altcoins trading paired with BTC. For example, I trade in pairs such as: TRX/BTC, XLM/BTC, EOS/BTC, HBZ/BTC. You can choose one of these trading pairs or find your own, which will be convenient for you. Thus, you will increase your balance in BTC or altcoins, if necessary, sell for USD and cash out.