Chris Davies of SlashGear is reporting that Apple Music will stream at 256kbps -- the same as iTunes Match and most iTunes Store tracks. The report does not mention which codec Apple Music will be using. However, it's likely that it will be 256kbps AAC (which is what iTunes/Apple current uses). That's generally better sounding, or equal to 320kbps MP3.
For comparison, Beats Music streams at 320kbps MP3 or HE-AAC 64kbps on mobile. Spotify uses a variety of different bitrates, encoded through Vorbis: 96kbps for mobile and 160kbps for desktop. If you're a Spotify Premium user, you get 320kbps on any platform. Jay'z Tidal music service offers 320kbps for $10/month and HiFi Lossless streaming for $20/month.
Regardless, it is highly unlikely that the human ear can hear the difference between any of these services with standard audio equipment.
Apple Music, featuring Beats 1 Radio, Connect, and more, will launch June 30 with the release of iOS 8.4.