I would never invest in centralised coins like Ripple, because I think such coins are killing the idea of blockchain and crypto currencies in general. Stable coins like Tether are centralised as well, so I would stay aways from such "cryptocurrencies".
XRP is really good if you just want much faster transactions you can use it instead of BTC and the transaction fee is much lower if you compare. stable coins such as tether is also a big help in the market you dont need to convert it directky to fiat if you already have tether.