Depends on your duration of investment and risk profile. By the coins you mention I'm guessing long duration, low risk.

I would choose ETH 60%, BTC 30% and LTC 10%. I don't see a huge future for LTC, it has nothing special going for it. BTC is too big to grow much, but it is the ultimate store of crypto value. ETH still has room for much growth. Ripple is the devil in coin form. I won't touch it.