If I were to choose only one from XRP and XLM, I would most certainly go with XRP. Also XRP has shown greatest volatility, and that is where the greatest opportunity lies for making money, at least in the short term. Sure, everyone would like to buy a coin for pennies, and have it turn into a Bitcoin, but in reality, that is rather rare to say the least. I would not hold my breath for either XRP or XLM to turn into a Bitcoin with respect to price.