Amazon's free music storage is virtually the same as Apple's: Any songs you purchase through Amazon are stored for free. But, if you want to be able to upload more than 250 of your own digital files to Amazon's music library, you've got to pay for their premium music service, which costs the same amount as iTunes Match.
One advantage to Amazon's Music offering is that they will let you import 250,000 songs (10x as many as iTunes Match) for that $25/year price. Unfortunately, the matched versions on Amazon's service are streamed back to you in MP3 format, rather than AAC like iTunes Match. This has a detrimental effect on battery life on any iOS device as they support hardware decoding of AAC. This is also true of Google's music matching service, as well.
The big advantage to Google's new initiative is that it makes iTunes Match look antiquated. 25,000 tracks for a fee is a lot less appealing than 50,000 for free. iTunes Match's strongest suit remains its integration into the iOS and OS X ecosystems. But, I can certainly see users being willing to jump through a few hoops to get access to their music via Google's music service to save $25 a month, especially if their library is larger than 25,000 songs.
Most any device decodes aac. Battery life of aac being better at decoding is non existent.