Sure ADA has potential but Ethereum is already established and has one functional DAPP on it. ADA is smoke and mirrors right now and has provided nothing other than hype. Hilarious how everybody loves to hop on the hype train, but nobody wants the real stuff train.
I think selling all the ETH for an ADA is a bad decision. If you want to sell it, sell some to buy ADA or to buy another coin. If you want to invest in another coin it is a good choice, by investing into another coin that will certainly reduce the risk if one of the coins decreased drastically you will not suffer huge losses. But it all depends on you, do what you think is right.