Wednesday, 23 July 2025

How to Choose the Right LLM (Large Language Model) for Your Project

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The rise of Large Language Models (LLMs) like GPT, Claude, Mistral, LLaMA, Gemini, and open-source models like Mistral and Falcon has transformed the AI landscape. But with so many options, how do you choose the right LLM for your use case?

Whether you're building a chatbot, summarizing documents, doing code generation, or deploying AI at the edge, this blog will walk you through how to choose the best LLM, with real-world case studies.


Step-by-Step Framework for Choosing an LLM





1. Define Your Use Case Clearly

Ask:

  • Is it conversational AI, text classification, summarization, code generation, or search?
  • Do you need real-time responses or batch processing?
  • Is your priority cost, speed, accuracy, or customization?


2. Choose Between Hosted (Closed-Source) vs Open-Source

Hosted Models (e.g., OpenAI GPT-4, Claude, Gemini):

  • Pros: Reliable, powerful, easy to integrate (via API)
  • Cons: Expensive, less control, limited fine-tuning

Open-Source Models (e.g., Mistral, LLaMA2, Phi, Falcon):

  • Pros: Full control, customizable, on-prem deployment
  • Cons: Setup effort, resource heavy

3. Consider Model Size & Latency

  • Do you need a 7B model or a 65B one?
  • Larger ≠ better: sometimes tiny models (Phi-2, TinyLLaMA) perform well with the right tuning.
  • Use quantized versions (int4, int8) for edge or mobile inference.

4. Evaluate Fine-tuning and RAG Capabilities

  • Need to embed your documents? Look for models that support Retrieval-Augmented Generation (RAG).
  • Need domain-specific language (legal, medical)? Look for LoRA or instruction-tuned models.

5. Check for Ecosystem Support

  • Can it be deployed via Hugging Face, LangChain, LLamaIndex, or NVIDIA Triton?
  • Does it support tool calling, function calling, streaming, or multimodal input?


Case Studies: Picking the Right LLM

Case Study 1: Internal Knowledge Assistant

Use Case: Build a private chatbot over company documents
Chosen Model: Mistral 7B Instruct with RAG + LangChain
Why:

  • Fast and lightweight
  • Easy on-prem deployment
  • RAG support with vector DB (e.g., FAISS)
  • Avoided cloud compliance issues


Case Study 2: AI Coding Assistant

Use Case: Autocomplete + Explain + Generate code (JS, Python)
Chosen Model: GPT-4 (fallback: Code LLaMA 13B)

Why:

  • GPT-4 has top-tier code understanding
  • Fine-tuned for reasoning and explanations
  • Code LLaMA used for cost-effective offline inference


Case Study 3: Customer Support Chatbot

Use Case: E-commerce support bot with FAQs + order tracking
Chosen Model: Claude 3 Sonnet + function calling
Why:

  • Supports long context windows (100k+ tokens)
  • Sensitive to safety and tone
  • Function calling triggers live API access (for order status)


Case Study 4: Edge AI on Mobile App

Use Case: Summarize voice commands on-device
Chosen Model: Phi-2 (2.7B) quantized to int4
Why:

  • Tiny, fast, accurate
  • Runs locally with 2GB RAM footprint
  • No internet needed = privacy-safe


Case Study 5: Document Summarization for Legal Tech

Use Case: Auto-summarize lengthy legal PDFs
Chosen Model: Gemini Pro (fallback: LLaMA2 13B fine-tuned)
Why:

  • Gemini handles long contexts efficiently
  • Model outputs are more extractive and accurate
  • Backup on-prem version ensures compliance

Tools to Compare Models


Choosing the right LLM is a balance of trade-offs: performance, cost, openness, latency, and domain relevance.

No one-size-fits-all model exists test, benchmark, and iterate based on your needs.

In Shorts

Use Case Best LLM Option
Chatbot w/ API Calls Claude 3 / GPT-4 w/ Tool Use
Offline Summarizer Phi-2 / Mistral 7B Quantized
Legal or Long Docs Gemini Pro / Claude 3 Opus
Dev Copilot GPT-4 / Code LLaMA
Custom On-Prem Chat Mistral 7B / LLaMA2 w/ LangChain

The world of Large Language Models is vast, rapidly evolving, and full of potential but choosing the right one for your project requires clarity, experimentation, and alignment with your technical and business goals.

Whether you're building a customer-facing chatbot, an internal knowledge tool, or a real-time assistant for edge devices, the best LLM is the one that strikes the right balance between performance, cost, customizability, and deployment feasibility.

Start with your use case, test across a few top candidates, monitor performance, and adapt.
As the ecosystem matures, staying agile and LLM-aware will give your projects a competitive edge.

Remember: it’s not about using the biggest model it’s about using the right one.


Bibliography

  1. OpenAI. GPT-4 Technical Report. OpenAI. Retrieved from https://openai.com/research/gpt-4
  2. Anthropic. Claude 3 Models. Retrieved from https://www.anthropic.com/index/claude-3
  3. Google DeepMind. Gemini 1.5 Technical Preview. Retrieved from https://deepmind.google/technologies/gemini/
  4. Meta AI. LLaMA 2: Open Foundation and Fine-tuned Chat Models. Retrieved from https://ai.meta.com/llama/
  5. Mistral AI. Mistral & Mixtral Model Cards. Retrieved from https://mistral.ai/news/
  6. Microsoft Research. Phi-2: A Small Language Model with Big Potential. Retrieved from https://www.microsoft.com/en-us/research/project/phi/
  7. Hugging Face. Open LLM Leaderboard. Retrieved from https://huggingface.co/spaces/HuggingFaceH4/open_llm_leaderboard
  8. LangChain. Documentation and Integrations. Retrieved from https://docs.langchain.com/
  9. OpenRouter. Compare and Route LLMs. Retrieved from https://openrouter.ai/
  10. LMSYS. Chatbot Arena – LLM Benchmarking. Retrieved from https://chat.lmsys.org/

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