Picking your first harness
Pick based on where you already work. If you live in a terminal, start with Claude Code. If you live in an editor, start with Cursor or Cline. That decision matters less than people think, because the underlying models are largely the same and switching later costs you an afternoon.
The honest summary
Most harnesses call the same handful of frontier models. The differences are in how they manage context, how they handle permissions, and how they fit your existing habits. None of them is dramatically better at writing code, because the model does that part.
Do not spend a week evaluating. Pick one, use it for a real task, and change if it annoys you.
The main options
Claude Code runs in your terminal. It reads and edits files in your project, runs commands, and asks permission before doing anything consequential. Good if you are comfortable in a shell and want the agent to work across a whole repository. Requires an Anthropic subscription or API access.
Cursor is a fork of VS Code with agent features built in. You get an editor you already know, with inline suggestions, a chat sidebar, and an agent mode that edits across files. Good if you want to stay in a familiar editor. Free tier available, paid tier for heavier use.
Cline is an open source VS Code extension. You bring your own API key, which means you pay providers directly and can see exactly what each task costs. Good if you want control and transparency, and do not mind more configuration.
Continue is another open source extension, for VS Code and JetBrains. Strong if you use JetBrains editors, where the options are thinner.
Codex is OpenAI's coding agent, available as a CLI and in the cloud. Sensible if you are already committed to the OpenAI ecosystem.
Aider is a terminal agent built tightly around git. Every change becomes a commit, which makes undo trivial. Good if you think in commits and want a clear audit trail.
How to actually choose
Ask three questions.
Where do you already work? Terminal people are happier with Claude Code or Aider. Editor people are happier with Cursor, Cline, or Continue. Fighting your own habits to use a tool is a bad trade.
How do you want to pay? Subscription pricing is predictable and usually cheaper for heavy use. Bring your own key is pay as you go, transparent per task, and can get expensive quickly if you leave an agent running on a large codebase.
How much control do you want? Open source options let you see and change the loop. Closed products make more decisions for you, which is often what you want at the start.
What does not matter yet
Benchmark scores. They measure narrow tasks and do not predict how a tool feels on your codebase.
Feature checklists. Every harness is shipping fast, and a feature missing today may exist next month.
Model choice. Most harnesses let you switch models, so it is not a permanent decision.
A reasonable default
If you have no strong preference and want one answer: start with Claude Code if you are comfortable in a terminal, and Cursor if you are not. Both are mature, well documented, and easy to get running in under an hour.