Which is the best altcoin exchange
I think that the best service will be the one that does not require registration and account creation. Many have problems with blocking accounts, so you can lose your funds.
You already described changenow

Of course, it is possible for the centralization of cryptocurrency and trading platforms to bear certain opportunities for users of cryptocurrency. Exchanges such as ether delta or forkdelta are exactly what will never allow the user to lose their account and their funds. Nevertheless, there are quite a lot of trading platforms with SMS confirmation, which provide security guarantees. Although I like exchangers without confirming personal data.
Forkdelta and etherdelta are both decentralized exchange . exchanges like these are risky because they dont ask for registration ( e.g username and password ) instead they will only ask for your private keys . you must import your private keys on thier platform before you can start trading .
With these kind of exchange , they are also popular for phishing sites because phishers can easily access all your cryptos if they have a control to your private keys . beware !