I can't tell you one app is the best for everybody, but the free one I'd start with is ChatGPT, because you upload your own product photo and ask for the ad in the chat. OpenAI says image creation is on every ChatGPT plan, the free one included, and you can get any shape with the aspect ratio picker or by saying it in your prompt. The catch is the limits. On Free, image creation has its own cap and ChatGPT tells you when you hit it, and you only get three file uploads a day, so I'd upload the photo once and make everything in that chat.
So what I'd do is test it on one real photo before you pay for anything. Pick a clear shot of what you sell, like a window on a clean wall or a water heater in good light, and ask for a minimal poster with no words on it. If the product still looks like your product, you got your answer for free. If you like it and keep hitting the limit, Go is $8 a month and Plus is $20 on OpenAI's pricing page as of October 31, 2026. The three prompts I use and the check I run before anything posts are in my guide to turning one photo into three ads.
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