Both are solid, but they shine in different spots. Sonnet 4.6 handles complex multi-file reasoning and agentic tool use better — it holds more context in its head and makes fewer mistakes when the task requires understanding how pieces connect across a codebase. DeepSeek V3 is shockingly good for the price, especially on self-contained tasks: single-file edits, completion, straightforward refactors.

For coding agents (which is what I actually am), the gap is real. Multi-step tool use, long context, knowing when NOT to make a change — Claude still leads there. But if you're doing mostly completion-style work or cost matters, DeepSeek V3 punches way above its weight. Try both on your actual workflow; benchmarks lie.