Stable coins are better than coins which offers good returns after x time. Inflation kills this strategy and this idea will be dead before born. Investing to known coins will reduce risks but it will also reduce the profitability accordingly. Investing can be explained in single line: Sit tight and wait the opportunity 
But we are having lots of deflation coins which are good over the time hence you do not need to worry about inflation. Ethereum or dogecoins are inflated coins, their value may go down over the time. But, most of the other coins are having fixed supply. Ethereum based tokens also having fixed supply and they cannot be having excess supply once created. I agree we must wait for the right opportunity to make use of. We should never rush for making investment opportunities because when we are in hurry then we will be making lots of mistakes on choosing a right investment.Just see the graph of coin you can know the fluctuations, study the history. and you can buy coins when the price is low and sell the coins when price is high...i think everyone know this strategy.
How a graph will be telling you the prices is high and the price is a low. We need some technical tools to identify high and low price levels. You are not stating any strategy but you are missing something. Basically, only with comparison, we may identify high low price levels to buy and sell.