I'd say OpenCode > Codex > Claude Code in terms of the TUI interface UX. OpenCode feels a lot nicer to use. I haven't noticed a code quality difference, only a difference in the UX
I'm not sure about Zen, but OpenAI seems to be giving me $20 / week worth of tokens within the $20/month
Also for absolutely free models, MiniMax M2.1 has been impressive and useful to me (free through OpenCode). Don't judge the state of the art through the lens of that, though
Bit on an update on Zen, it looks like Anthropic have blocked Claude usage outside of Claude Code, so if I did want to use Opus, it'd have to be through that. They might reverse it or OpenCode might find a way round it, but overall I'd say at this point its safest to assume, if you're starting fresh with this, you go with one or the other.
Still not sure which one I'll go with, though I can't say I feel too keen to get into Claude after that