I use langchain.js , and I like its composability and availablilty of different readers or database drivers with it

Langchain is the best framework for building RAG applications its supports all find of Large Language Models that is both open-source like llama, mistral and closed-source models like OpenAI, and Anthropic using their Access token. It also supports using local LLMs using the Ollama. I build RAG application for our enterprise data using it , its very simple to build and it has many features like a chain of thoughts and memory. They have clean documentation which we can refer to and add more features. We can easily integrate with their other products like Langsmith and Langgraph

It is one of the best packages required to use Large Language Models in the field of Generative AI, it is easy to adapt and works like a charm and it keeps upgrading itself to be compatible with the latest technology