I believe that eBird is more user-friendly, as others have said.
The main reason that I use eBird over Birdata is that you can find out which species were seen at a specific location, and the photos to go with it.
Birdata is fine if you are targeting one species, but not if you are interested in what birds you migt see when you are going somewhere or other.
Drew Davison
Here's a BirdLife statement about the two data entry systems, both of which are acceptable for the bird atlas 20min-2ha, 500m radius earch, and 5km radius search methods.
https://ebirdorg/australia/news/birdlife-surveys/
OK eBird data is only transferred to the Atlas quarterly but that won't make much difference to the scientific use of the data
I encourage people to use eBird because it helps the general public.
I believe the data is also transferred to the Victorian Biodiversity Atlas but have not yet got that officially confirmed.
Michael Norris