This link points to a "multiplexer" site which parcels out requests to various up-to-date CTAN mirrors. Occasionally users have trouble getting the package from this multiplexer. In that case, choose a specific mirror on this mirror page.
Was the download successful?
There is an easy way to check that your download was successful. Run Apple's Terminal application in /Applications/Utilities. After the prompt, type the command
and add a space at the end. Then drag and drop the file MacTeX.pkg to the Terminal window to complete the command. Push Return.
The Mac will compute an "MD5 checksum". The correct sum is shown at the top of the downloading page here.
Change the word md5 to sha512 in the previous command to check the Sha512 sum, also shown on the linked page above.
What to do if the Checksum is bad
Many users report trouble after downloading with Google Chrome,
and possibly other browsers. We strongly recommend downloading with
Safari. Users with problems also report success after downloading
via the torrent network.
What to do if the Installation Succeeds but TeX Doesn't Work