Harness Question with v4 Pro

What harness do you guys use for v4 pro when coding? My project was planned using grill-with-docs, it has docs planned out for every single feature then I started the project with Claude Code (Opus 4.8) and Codex (GPT-5.5). Then halfway through the project, I was curious about DeepSeek because there’s so many claims that it’s very cheap to use. So I used the DeepSeek API and loaded 2$ and used Opencode as my harness. I was excited because I thought it would be as good as GPT-5.5 or Opus 4.8 but it’s far fro