What is the best framework for RAG?

What is the best framework for RAG on private data? Initially using OpenAI is fine, but ideally seamless support for open models and fine tuning if I want to migrate from RAG. Data is in JSON format. I’m open to using Python or Go, or even TS/JS so language is not an issue.

I am using llamaindex with pgvector and OpenAI and it works well. But with new options being launched everyday, just wanted to ask if there were better options that were up and coming.