I strongly believe in most of them, specially the ones that have a strong background, website, white paper, and support. From the ones mentioned above, XRP (Ripple) is quite interesting. There are many others that use the blockchain technology that have a very appealing idea of what the future beholds.

• Golem, for example, is a decentralized supercomputer that will allow user's machines to combine power around the world and compute any program you can think of.
• IOTA, is the perfect example for the "internet of things"
• Siacoin will let you save your files on someone else's computer on a decentralized future

All of these and many more have very interesting background to look into.