which is the best approach to send push notification to android & iOS devices

I am developing a ticketing application for Android & iOS devices. When some action is taken against a ticket, ticket creator should be be notified via a push notification.The notification is not general, but should be delivered to a unique android or iOS device. So which is the best approach to implement it ? I found multiple solutions in internet, Solution 1: Use Google's GCM for Android & iOS Solution 2: Use Amazon's Simple Notification Service (SNS) for sending the push notification to Android & iOS Solution 3: Use Firebase Cloud Messaging(FCM) for Android & iOS Also there are many open source/frameworks for cross-platform push notification. As per my understanding, I prefer FCM. Is there any usage limit for FCM ? Which is the best approach or framework to follow ? Any suggestion is highly appreciated. I am looking for a cost effective solution.