Use what you know......thats what myself and Jon do.
Jon will soon be re-writing my site in ASP.NET, at the moment it runs in just basic asp.
The big difference main difference between to two as far as i can see (apart from the code itself

) is that most PHP stuff (scripts,tools) is free whereas asp.net you tend to have to pay for.
We try to write as many scripts as we can ourselves, you can bever really fully customise somebody else's script for your own site.
The one thing we like about asp is database stuff seems to be a doddle and if you use an Access database it can be sorted on the desktop and then sent to the server....
.NET still goes wooosh over my head but Jon is starting to get to grips with it.
I think Jon (another one) from Natural Instinct uses asp.net a lot......he may have some ideas....
Carol