Quite frankly, the VHD approach would be the same as the ISO approach, in my opinion.
The WAIK/MDT approach takes the WIM file (which is basically an image of a C:\ drive) and applies it to a hard disk, then makes it bootable. To use this approach, you can use WAIK to capture an "image" of the modified OS (after its been installed) with anything else that happens to be on the drive, and dumps it into a WIM file. Then, MDT packages this WIM file into Windows Setup, in which you can deploy attended or unattended. However, I don't see what the point of this is when you already have the modified ISO.
The VHD approach, from what I think you're saying, is that you place the VHD on each workstation of laptop and then boot from it as a virtual hard drive. Copying the VHD over to each device will take a while, not to mention that the client then has to be configured to boot from the VHD, which takes a little longer, while Windows Setup does it all automatically on the ISO approach.
I've tried using the ISO approach to deploy my own Windows installation, but ran into some hiccups, so I'm not quite clear either exactly how well it works.