Which one is a better investment, Bitcoin, Ethereum, Litecoin, or Ripple?

It depends on what you want to invest in.

A store of value
A technology ecosystem
A communications protocol
A hedge

Let me explain.

If your primary interest in investing in cryptocurrencies is driven by a concern with the stability of the fiat monetary system than you should invest in Bitcoin.

Ethereum appears to be trying to build an ecosystem around the concept of smart contracts. Similar to how the app store serves as a distribution mechanism for app developers. Ethereum is looking to be the gateway to access a wide variety of applications via one convenient piece of technology.

As of now the only way to access these services is with Ether. Betting on Ethereum is betting on Ether going up in value. Because the network of services it provides access too grows and becomes more valuable over time.

Ripple is looking to carve out a piece of the behind the scenes communications between large financial institutions currently dominated by competitors like SWIFT (Society for Worldwide Interbank Financial Telecommunication).

Investing in Ripple is betting on its ability to offer a better mousetrap appealing to large financial institutions that will get you a small piece of a large pie.

In terms of the challenge it faces think of it in terms of plumbing. It takes a lot for you to replace the pipes in your home. If you do though it is quite lucrative for the plumber.

And if a pipe springs a leak you may call the plumber to patch only the leaky section. Which at least allows the plumber to pay his bills.

Litecoin is an attempt to resolve some of the challenges Bitcoin faces with processing large volumes of transactions in a timely fashion. If you own Bitcoin it is a nice hedge if you are concerned with Bitcoin overcoming these challenges.

And even if Bitcoin does overcome these challenges it could still have some value in its own right from the value created by the Lightning Network as a payment facilitator.