For instance, if you were developing an online shares dealing portal, then security and stability would be major considerations.
In this case, you may well be somewhat concerned about relying on Microsoft technologies. Recent virus scares have highlighted security holes in some of Microsoft's products.
Therefore, Java and Java Server Pages may be better suited to your needs. Multi platform support may also be an issue with Microsoft technologies.
On the other hand, your web application may be less mission critical, but need to be developed quickly. You may also be looking to rapidly expand the web application in the near future.
In this case, Microsoft technologies might better suit your needs. This is particularly true if you are already using IIS and development environments such as Visual Studio.
Then again, you may not have much in-house development experience. Perhaps you want your graphics designers to also do the programming.
In this case, Cold Fusion or even PHP may fit your needs.
There is no hard or fast rule which dictates which web technology or web architecture best fits your requirement. It is necessary to take a step back, examine your current and future needs. Then examine your current infrastructure. Only after you've done this can you hope to make a balanced decision.
Tip: try and make your decision based on the facts and relative merits, rather than someone's biased opinion.