As a user, I've found that researching the same topics in OpenAI Deep Research vs Perplexity's Deep Research results in "narrow and deep" vs "shallow and broad".
OpenAI tends to have something like 20 high quality sources selected and goes very deep in the specific topic, producing something like 20-50 pages of research in all areas and adjacent areas. It takes a lot to read but is quite good.
Perplexity tends to hit something like 60 or more sources, goes fairly shallow, answers some questions in general ways but is excellent at giving you the surface area of the problem space and thoughts about where to go deeper if needed.
OpenAI takes a lot longer to complete, perhaps 20x longer. This factors heavily into whether you want a surface-y answer now or a deep answer later.
OpenAI tends to have something like 20 high quality sources selected and goes very deep in the specific topic, producing something like 20-50 pages of research in all areas and adjacent areas. It takes a lot to read but is quite good.
Perplexity tends to hit something like 60 or more sources, goes fairly shallow, answers some questions in general ways but is excellent at giving you the surface area of the problem space and thoughts about where to go deeper if needed.
OpenAI takes a lot longer to complete, perhaps 20x longer. This factors heavily into whether you want a surface-y answer now or a deep answer later.