Begin with the task
The best model depends on what the product must accomplish. A coding assistant, document search system, voice agent, and image workflow have different requirements, even when each one uses generative AI.
Define a small evaluation set from real user requests. Include ordinary cases, difficult cases, and examples where an incorrect answer would be costly.
Compare more than output quality
Quality matters, but latency, context window, structured output reliability, tool use, and price can change which model is practical. A smaller model may be the better production choice when it handles the common path quickly and consistently.
Multimodal products should also test the exact input and output types they need. Text, embeddings, images, audio, and video models require different evaluation criteria and may use different pricing units.
Keep the model replaceable
Model capabilities and pricing change frequently. Keep model selection in configuration, store evaluation results, and avoid coupling product logic to one provider-specific response format.
A unified API makes controlled comparisons and migrations easier because the surrounding application request format can stay consistent.