I'll say upfront that I am inherently biased, since I work on Azure.
But these are significantly different services.
Amazon SNS primary scenario is push to individual devices, or small groups of devices. You need to maintain the endpoints, and pre-create topics. You can do multicast with topics, but a topic afaik cannot have more than 10K devices, so you can only multicast to 10K users at a time.
Notification Hubs offers you segmented/personalized push engagement for millions of users. You can broadcast to unlimited # of devices with a single API call, you can manage segments/target arbitrary segment expressions, personalize/localize your pushes using templates, etc.
If you don't need any of the extra features Notification Hubs offers, and just need a simple push to individual devices, Azure pricing page advises contacting mobileservices@microsoft.com for low price offering for high volume individual push scenarios.