Eth and LTC are two of the top digital currency on date. It is a clever move of you're going to invest in these two top coins after Bitcoin. If you see side by side history comparison they're both reaching the top graphically.
Being top digital currency is not a criteria to consider them for long term investment purposes. We must look into the future of these coins so that we can make better conclusion to find which will be having more value in coming days. Based on this I am believing in to ETH because in recent times this alone is performing better so that I will be investing only with ETH.