During the deployment roadshow me and Johan did recently a recurring question was if it is possible to set the default boot image in WDS if one have multiple boot images.
Well of course you can set it, just go to Properties for the WDS server and go to the boot tab and choose a default boot image for the architecture you want to set a default image. Note: This sets the default boot image to the one you choose but you will still be able to choose another boot image in the list of boot images.