Most people pick a model the wrong way around. They look at the leaderboard, see Opus on top, and reach for it by default. Sonnet if they want to save money. Haiku almost never, because the name says "small."
That habit costs you. For a lot of what you actually build, Haiku is the right call, and you're paying three to five times more for capability the task never uses. This post is about how to choose, and why Haiku should be your default more often than it is.
The short version: don't start from "what's the best model." Start from "what does this task need." Most tasks don't need much.
Comparison
Here is the current lineup, with the numbers that matter when you're choosing.
