Leonardo AI usually wins for 300 thumbnails/month: stronger per-image cost control (credits, batch templates), granular params (seed lock, style tokens) and reliable batch rendering. Midjourney produces very consistent, high-quality artistic styles but is subscription-focused with less granular per-image pricing. To ensure repeatability: fix model/version + seed, use a template image and a private LoRA or prompt template, then run a 50–100 image test batch to measure cost and tweak prompts.

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