Picking the right Azure data centre to host your application in is critical to getting decent levels of latency. In some cases it's very clear which data centre to use based on your audience location, but what about when things aren't so clear? If your in Europe, which of the two locations is best? If your in the Middle East, where there are no Azure data centres, how do you find out which is the best to use?
Two10 degrees, an Azure consultancy, has come up with a very useful tool for testing the latency of accessing blob storage in each of the Azure data centres (and CDN) from the client that runs the test - http://azurespeedtest.azurewebsites.net/
Testing from my location in the UK seems to indicate a toss-up between West and North Europe, which is pretty expected given similar distances to Ireland and the Netherlands.