In my opinion the biggest two factors that make a crypto currency successful are market capitalisation and the trading fees. If the market is too small, or there are not enough investors and traders, than it is not likely that new investors are going to buy that coin. We want a coin that is being actively traded in larger sizes so we can buy and sell more easily. And the more trader there are the lower the bid/ask spread should be. As for fees, the more we trade a coin the more important it becomes that fees are not so high.