Coinbase recently announced that its customers in supported jurisdictions can send, receive, buy, and sell the USD Coin stablecoin (USDC) on its website and mobile applications. This marks Coinbase first entry into stablecoins, which have a fundamental difference as compared to other cryptocurrencies. A USDC is pegged to the price of a single US dollar (USD). Coinbase explains that one USDC is represented by one USD on the Ethereum blockchain.
Yes. Bitcoin has not been made illegal in any country to date, although some nations restrict its use more heavily than others. Bitcoin is often associated with crime, because it can be used to make criminal transactions. However, this is true of any currency. Bitcoin is harder for authorities to trace than digital fiat transfers, but easier to trace than cash, and most criminal transactions in the world are made with fiat, not Bitcoin.
Volatility is perhaps the most commonly-cited disadvantage of Bitcoin in terms of its use case as cash. Ironically, that very volatility helped grow the network, providing traders with very lucrative opportunities in short time periods. However, for those wishing to store value and transact Bitcoin as an everyday currency, the volatility is a major drawback.
Ripple positions itself as a complement to, rather than a competitor with, Bitcoin - the site has a page dedicated to Ripple for bitcoiners. Ripple is a distributed network which means transactions occur immediately across the network - and as it is peer to peer - the network is resilient to systemic risk. Ripples aren't mined - unlike bitcoin and its peers - but each transaction destroys a small amount of XRP which adds a deflationary measure into the system.