Both of those cryptocurrency are nice also as I've check. The main purpose for which ripple was created was to enable transaction with low fee but polkadot can be used in different areas most especially for staking which also gives better opportunity for people to make money . In a simple conclusion both of them are worth investing on if you have the money to do so.Both coins are actually good in their own way but if you're asking about making an investment choice between the two, I would probably go with the latter as the former is still having court issues I guess.