Meteor is a good tool for prototyping or writing very small apps quickly. But has a lot of downsides that I explained here: medium.com/@pierrebaz/why-i-won-t-recommend-meteo…

Firebase is composed of many building blocks:

• the free HTTPS hosting & deployment is awesome
• the JS file uploader to Cloud Storage is incredible
• the authentication layer with custom JWT is a must have
• the cloud functions with custom endpoints are the new PaaS
• the realtime database is maybe not what you are looking for: you can't apply complex filters on your queries, thus you have to denormalize your dataset to be able to query it in an efficient way. I would personnaly recommend to use the realtime database for simple use cases (chat...) & to trigger HTTP roundtrips to your real DB for your complex queries.

I'd go with GraphQL subscriptions and web sockets. I personally think Meteor is great for quick prototyping, but it's not suitable for production environments. Firebase would be a great alternative, but I think GraphQL subscriptions give you more control.

I'll go with Firebase because I can easily integrate it with my stack, which is not possible if I choose Meteor.