My honest take: I don't pick one model, I pick one per job, and that single shift saved me more money and grief than any benchmark ever did. For the reasoning-heavy parts of an agent, the planning, the judgement calls, the bits where one wrong turn cascades into a mess, I default to the strongest Claude I can justify. It's the most reliable I've used for staying coherent over long multi-step runs, which is exactly where most agents quietly fall apart. But the second a step is routine and high-volume, classifying, extracting, summarising the same shape of thing a thousand times over, paying top-model prices is just lighting money on fire. For those I drop to a smaller, faster model, and a fair chunk of it I run locally on my own box and pay nothing at all. So to your real question: no, there's no good reason not to make Claude your general-purpose default, it's a very strong all-rounder and a sensible place to start. The trap is using your most expensive model for every step inside an agent and then wondering why the bill and the latency are brutal once you scale. One more thing that took me far too long to learn: the model is rarely what's holding an agent back. Nine times out of ten it's the context I fed it and the tools I gave it, not the brain. A mid-tier model with clean context will beat a frontier model flailing around blind every time. Mix and match, and only reach for the big gun when the step genuinely earns it.