From various sources, MyEtherWallet (MEW) are not under development and maintenance any more. Even its founders has confirmed that they are switching to develop a new platform called mycrypto and encourage everybody to move there property to there.
But IMO, MEW or mycrypto is just a gateway to access your real wallet in the blockchain, so, both of them are still fine event MEW is not maintained anymore, right?
ERC-20 is the service I use most often for my tokens and to keep Ethereum themselves. Of course it would be a mistake to say that I kept a very high amount of money, but I can easily say that I use it extensively and that I am satisfied with this service. I do not yet have a security problem on my own but I do not want to go through without telling some friends around me that I have minor problems. Although I have friends who are not satisfied with this service around the time, I think it is quite handy and reliable for transactions up to a certain amount.