Hi,
First thing to understand is that mojoPortal is built on ASP.NET WebForms, so it is not an alternative to WebForms.
So the real question is should you start from scratch or build on top of some existing framework like mojoPortal. Obviously it will be a lot more work to build from scratch but ultimately you must make the decision yourself therefore you should do your own evaluation of mojoPortal and decide whether it will save you time and whether you find it approachable to develop on top of mojoPortal and whether you find it to be a suitable foundation for your projects.
Best,
Joe