If I were you, I'd be looking for the following features:

1. The ability to export the private key
2. The ability to set the transaction fee by yourself
3. Availability of 2FA
4. Positive reviews from the crypto users
5. Ability to store multiple crypto-currencies
6. Ease of use
7. Friendly UI
8. Mobile friendly
9. Extra protection from hackers
10. Based in a country where the services are legal

(the top 3 are the most important ones).