PubGalaxy names 2,599 sites in its seller file against Adnimation’s 563, and 17 sites appear in both files. Reach is only half the question though — the authority spread below shows what kind of sites each one actually carries, which is what determines whether you would be accepted and what the inventory is worth.
Adnimation is the more selective of the two, with a median authority of 30 against 18. Read the overlap with care. Two display networks rarely run on the same site, so most of those 17 are publishers part-way through switching, still listed by the network they are leaving. A video network listed alongside a display network is the exception — that is usually a genuine pairing.
On 2,036 more sites than Adnimation — the larger footprint of the two.
Median authority of 18 against 30 — more of its sites are still small, so a growing site clears its bar sooner.
Mostly sites mid-switch between the two, unless one is a video network that runs alongside display. The “Also uses” column on either network page lists them.