1. Price
Google's storage cost = 25c / Gigabyte / year = 2c / Gigabyte / month. There is no additional transfer cost.
Windows Azure's storage cost is at 15c / Gigabyte / month. There is additional cost for transfer data in and out.
Note: Google storage is clearly cheaper, about 10 times cheaper.
2. Speed
We will use Gladinet Cloud Desktop to map both in a virtual drive in Windows Explorer and compare the time it takes to complete a drag & drop upload task of each.
File Size: 9.3M
Azure Storage Upload: 43 seconds => 216 Kbytes/s
Google Docs Upload: 68 seconds => 136 Kbytes/s
Azure Storage is faster to upload. However, the 136 Kbytes/s is very decent upload speed too. The speed could also vary depending on whether you are close to a Google data center or a Microsoft Azure data center or which one is busier or less.
3. Usability & Tools
Google Storage is shared between Gmail, Picasa Web Albums and Google Docs, all of which have web interfaces to use and share with friends. For the desktop PC UI interface, you have client side GUI tools such as Google Picasa, Gladinet Cloud Desktop or Memeo Connect to connect your Google Storage account directly into your Desktop PC.
Azure on the other hand, is more geared toward developers. You won't be able to use Azure Storage until you write some code. You can use some 3rd parties' tools to use Azure Storage, such as Azure Storage Explorer, Cloud Storage Studio, Azure MMC plug-in, Gladinet and others.
Google Storage is more usable out of the box. However, Azure storage may have more tools available down the road.
Note: This may not be an apple-to-apple comparison in this aspect between Google Storage and Azure Storage. A better comparison may be between Google Storage and Windows Live SkyDrive when both have web interface.
4. Service Level Agreement
Google's SLA is different for free user, Google Apps user and Google Apps Premier Edition user. Below is a glimpse of what is offered for the premier account users, which may not be applied to free users.
"During the Term of the applicable Google Apps Agreement, the Google Apps Covered Services web interface will be operational and available to Customer at least 99.9% of the time in any calendar month (the "Google Apps SLA")."
Windows Azure SLA
"For storage, we guarantee that at least 99.9% of the time we will successfully process correctly formatted requests that we receive to add, update, read and delete data. We also guarantee that your storage accounts will have connectivity to our Internet gateway."
5. Developer Support
Google offers Google DATA Protocol for developers. Windows Azure offersAzure SDKs which integrates directly into Visual Studio.
It is much easier to program towards Windows Azure Storage with Visual Studio so you may see more tools and internet products built on top of Windows Azure further down the road.
However, if you are using PHP, Ruby or anything other than .NET, Azure SDK may not have a big advantage over Google APIs.
