Railblocks(XRB) is turning out to be one of the most important project of the crypto world. The huge potential and it's application can make it a competitor to the sleuths like Bitcoin and Ethereum. The very reason for it's success is the problem it is solving and so far has been very successful in it's approach to grow and appreciate.
The biggest feature of Railblocks that make it stand out of the crowd is that it's ability to completely remove the transaction cost and the time taken for transfer of XRB to almost instant. If we compare that to Ethereum and Bitcoin, it is way more efficient and credible.
The closest competitor of XRB is IOTA. Below is the difference between the two:
XRB vs. IOTA: These two are perhaps the best known, and most successful, Directed Acyclic Graph (DAG) cryptos so they're talked about often in the same discussion. XRB aims to "do one thing and do it well", i.e. serve as feeless, instant P2P electronic cash for value transfer. IOTA has other facets to it, most notably data transfer and micro-transactions for machine-to-machine (M2M) applications - hence the name IOTA.
Similar to RaiBlocks, IOTA nodes must expend some computing power to send transactions. In IOTA on a basic level, you verify two other transactions to send a transaction of your own. At least for the time being, IOTA has a centralized coordinator which the dev team promises to remove once the Tangle has enough transactions to be naturally resilient against spam transactions.
On the other hand with RaiBlocks, your wallet performs a Proof of Work (PoW) which is simply a hash calculation that takes several seconds on a modern device to send a transaction. This PoW doesn't inherently verify other transactions; its simply an anti-spam measure. Instead, double spends or attempts to "forge" the ledger are resolved by a delegated Proof of Stake (DPoS) system where nodes "vote" on any conflicts using the copy of the blockchain they've stored. Voting power is in proportion to the XRB a node has in its own wallet + XRB that has been delegated to it by other addresses as a "Representative." There is no centralized coordinator with RaiBlocks, but there are 8 "Official Representatives" maintained by the core team that new wallets are set to by default.
Not going to go into too much depth comparing the other coins, but here are few lines about each.
XRB vs. XRP: Ripple's payment network functions similar to the Lightning Network (LN) under development for Bitcoin, where your ability to pay someone is based on you being connected directly, or through intermediarie(s) that have extended you and all the hops in between enough "credit" to setttle the transaction. Essentially the banking system on steroids. Ripple has gained traction with financial institutions, including American Express and Santander using Ripple Inc.'s technology, RippleNet, for cross-border settlements.
XRB vs. XLM: Stellar is a spin-off of Ripple but managed by a foundation instead of a for-profit company. Jed, the co-founder was also a founder of Ripple; Over some strategic differences, he left the Ripple core team to found Stellar as a more socially minded version of Ripple whose mission is to "bank the unbanked" and solve remittances especially for those in the developing world. XLM has a key partnership with IBM where IBM is using Stellar as the native token for some of its blockchain solutions. Like Ripple, they have some tie-ups with banks also who have been using it to reduce cross-border settlement costs and delays. This year Stellar is trying to capture part of the ICO market as well, with a complete toolkit for launching an ICO on Stellar available (much lower fees and less complexity than implementing a smart contract on Ethereum).
XRB vs. BCH: Bitcoin Cash is Bitcoin with a 8MB block size instead of 1MB blocksize, meaning more transactions fit within a block (reducing fees) but increasing the storage needed to run a full node. BCH transaction fees are currently very low, and it's not unheard of getting into the next block by paying as low as 1 Satoshi/byte. However, many see increasing the block size as a "band aid" solution to solving high fees. With the big blocks, BCH can accomodate somewhat more transaction throughput but would eventually run into the same problem as BTC if it gained more popularity. Although storage hardware falls in price each year, it would likely not fall quickly enough to make running a full node practical to the average user, in a mass adoption scenario for BCH. Unlike Bitcoin Core, Cash has not implemented Segwit, nor is it expected to add layer 2 scaling solutions such as Lightning Network.