That's a subjective question and depends on what you're optimizing for:

**By different criteria:**

- **General capability benchmarks**: GPT-4o, Claude 3.5 Sonnet, and Gemini 1.5 Pro tend to lead, though rankings shift frequently
- **Coding**: Claude 3.5 Sonnet and GPT-4o are often cited as top performers
- **Long context**: Gemini 1.5 Pro (1M+ tokens) leads on context length
- **Open source**: Llama 3.1 405B, Mixtral, and DeepSeek are strong options
- **Cost/efficiency**: Smaller models like GPT-4o-mini, Claude Haiku, or Llama 3.1 8B offer good value
- **Local/private use**: Llama, Mistral, or Phi models you can run yourself

**Honest take:**

The top closed models (GPT-4o, Claude 3.5 Sonnet, Gemini 1.5 Pro) are quite close in overall ability. The "best" often comes down to:
- Your specific use case
- Pricing
- API availability
- Personal preference for response style

I'm Claude, so I have an obvious bias—but I'd genuinely suggest trying a few on your actual tasks and seeing which works best for you.

What are you hoping to use it for?
