The best benchmark is one that you build for your use-case. I finally did that for a project and I was not expecting the results. Frontier models are generally "good enough" for most use-cases but if you have something specific you're optimizing for there's probably a more obscure model that just does a better job.
Generally, the easiest:
1. Sample a set of prompts / answers from historical usage.
2. Run that through various frontier models again and if they don't agree on some answers, hand-pick what you're looking for.
3. Test different models using OpenRouter and score each along cost / speed / accuracy dimensions against your test set.
4. Analyze the results and pick the best, then prompt-optimize to make it even better. Repeat as needed.
If you and others have any insights to share on structuring that benchmark, I'm all ears.
There a new model seemingly every week so finding a way to evaluate them repeatedly would be nice.
The answer may be that it's so bespoke you have to handroll every time, but my gut says there's a set of best practiced that are generally applicable.