Did you ever have to choose between WISA or LAMP at the beginning of a web project?
While pros and cons are littered around the net, it would be helpful to know about your real experience in coming up w/ criteria, evaluating, deciding, and reflecting upon your decision to go w/ either platform.
I think the first part is your Application. If you decide to go PHP, you almost automatically end up with LAMP, as WIMP or WISP stacks are quite rare (I think blog.stackoverflow.com runs on WIMP), and with .net you definitely want to go WISA.
So normally, it boils down to .net vs. PHP. (Ignoring Ruby, Python and all the other stuff for a moment). When you made that decision, the rest comes naturally or adapts into your environment (i.e. if all your admins in the company are windows admins, maybe WAMP works better for you)
I switched from PHP to .net about a year ago and I never looked back at PHP, but I never had to look at the bill for Windows and SQL Server licenses to be fair. Deployment on WISA has a much higher initial cost due to the licenses involved, whereas a LAMP Stack is free (Yes, MySQL is also free for commercial use).
Addendum:
All the funny acronyms stand for the combination of technologies: (L)inux or (W)indows, (A)pache or (I)IS, (M)ySQL or (S)QL Server, (P)hp or (A)SP.net.