It depends on what you need most.
GPT-5.2 is generally better for:
Coding and debugging
Deep reasoning and structured answers
Writing quality and instruction following
Complex conversations and analysis
Gemini 3 Pro is often better for:
Google ecosystem integration
Fast multimodal tasks (images, docs, video)
Large-context workflows
Lower-cost/high-volume usage in some cases
For most users:
Choose GPT-5.2 if you want the strongest overall chat, coding, and reasoning performance.
Choose Gemini 3 Pro if you heavily use Google tools or need strong multimodal features with competitive pricing.
Both are powerful, but GPT-5.2 is usually preferred for accuracy and coding, while Gemini 3 Pro is strong for speed and Google-connected workflows.