My favorite: - Procedural PHP / static calls - Lightweight NoSQL DBAL (I use MongoDB under the hood but any key/value store would do) - Vanilla JS on the Client - Plain CSS witout preprocessors
Since I do a lot of JS on the client I am quite happy not to have it on the server as well - also I dont like that npm madness / complex infrastructure around it.
Where do you tend to?
Use the stack with which you are most familiar with and get the product shipped.
The right stack is the one you already know. If you don't have such a stack already, the right one is probably the one that it's easiest to recruit/hire people for.
Like @slap_shot says, get something shipped. You should be so lucky as to be successful enough to have to worry about scalability. If you get to that point, you'll probably have enough money to hire enough developers to rewrite it anyway.
That said, here's my personal choice (what we use at Fogbeam):
Web application / server-side: Grails
Web application / client-side: mostly plain old HTML/CSS and some jQuery.
Backend services: mostly Java, running as services deployed as OSGi bundles in ServiceMix. JAX-RS using CXFRS for RESTful services, gRPC for RPC. JMS with ActiveMQ for async messaging. Camel for message routing.
Cloud providers: AWS (EC2, S3, Route 53) for deployment of customer facing applications. Linode for internal apps and basic infrastructure.
Databases: Mostly Postgresql.
Operating systems: Linux, mostly CentOS.
Build tools: Maven