Bitcoin Cash is the most popular Bitcoin hard fork proposed by Roger Ver in 2017 as a solution to the problem of slow transactions in the Bitcoin network. The idea was to create a version of Bitcoin that would be better for payments, while original Bitcoin is considered more as a store of value. Bitcoin Cash has a bigger block size than Bitcoin so the transactions of this currency are faster and cheaper. On the other side, it requires more resources to run the full node of Bitcoin Cash which makes it more vulnerable to centralization.
Bitcoin Cash quickly attracted a huge following and became a prominent part of the cryptocurrency market. BCH is available on many exchanges and is supported by numerous crypto services. Since the launch of the project, it has never left the top 10.
Dash was launched in 2014 and changed several names before becoming Dash as we know it today. The initial goal of the project was to create a cryptocurrency network which would operate faster and cheaper than Bitcoin and would be capable to maintain more privacy. Holders of large amounts of Dash have different privileges (Instant Send, Private Send, etc).
Dash is an open-source project. It has its own blockchain. The currency is supported by many crypto wallets and it has gained significant market capitalization. Another great achievement is its numerous partnerships including cooperations with Western Union, web stores, etc.