IME it entirely depends on your work. I find myself using both daily for different things.
Codex with GPT 5.5 is much better at general SWE tasks but Claude Code with Opus is far better at complex reasoning tasks like reading and summarizing research papers, replicating experiments, identifying research gaps and proposing interesting follow ups.
X is excellent for following niche research interests but they’ve been pushing quite hard to force political news/opinions into the feeds which is really annoying.
IME the most noticeable performance boosts are in complex multi-agent workflows.
EX. You call an orchestration agent and define an implementation plan with the help of a number of sub agents planning out different features. You and the lead agent review all of the plans and send them off to a set of agents that write tests which get send back to the orchestrator then passed along with the plan to a set of coding agents who implement the features in their own worktrees. That gets passed back to the orchestrator which hands it off to another set of agents doing the code review and merging the features before sending it back to you.
You could say the same thing about any always online software suite and it would be equally fair as we move into more agentic development workflows.
EX. Sure, you could go back to the old ways of using a drafting table for your engineering work if CAD went down but it would be exponentially slower…
Personally with my workflow I spend 30-60 minutes per Claude feature spec doc when I’m pair planning. If Claude goes down I would just prepare spec docs on my own until it came back online and then rapidly review them before calling the coding workflow.
Codex with GPT 5.5 is much better at general SWE tasks but Claude Code with Opus is far better at complex reasoning tasks like reading and summarizing research papers, replicating experiments, identifying research gaps and proposing interesting follow ups.