If volatility is your only parameter, then why don't you go for Ripple (XRP)? The legal battle with SEC is still ongoing, and when some ruling is made against them, you can expect the XRP exchange rates to go down by 60% or 70% (it has already happened multiple times). You can accumulate using these dips, and then sell when the prices are back to the normal levels. Another coin that comes to my mind is Dogecoin, but it is too overpriced right now. You can also go for BCH or ETC, if you are OK with more moderate gains.