If I personally prefer to invest in XRP, because XRP is already superior to XLM from the ranking on coinmarketcap, so this proves that more people believe to investing in XRP than XLM and of course the volume of XRP is also higher than XLM, therefore it will be possible if the price of XRP increases higher than the price of XLM in the future, so I prefer you to hold your XRP rather than XLM.
The ranking usually does not mean anything as it keeps on changing. The price of both these alts have risen a lot and now we have seen a major correction in XRP. If you want to invest in it or any other coin then these are the opportunities to hold them during major corrections rather than investing when the rally started, even still i would move away from those at this point because they had its rally in this market and everyone will be eyeing in bitcoin and ETH.
If you really want to choose between XRP and XLM right now, I guess many will opt for XLM. XRP is in the brink of falling down hard. We don't know what will happen to the SEC's lawsuit and how the XRP team can rectify this situation. Kind of dangerous to venture in XRP right now.