We're happy users of both Serverless Framework as well as SAM (AWS). Serverless Framework offers a pretty rich set of plugins which provides a lot of extensibility out of the box including function warming, webpack, instrumentation and many others.
Shameless plug alert: we also dogfood IOpipe, our own dev tooling for Lambda. IOpipe[1] gives us near realtime errors, logs, tracing, and CPU/mem profiling capabilities that we're used to having in "traditional" development environments.