In terms of development speed, which would be faster: webforms or mvc?
This depends on many factors, but suppose that you use eqal technologies both with webforms and mvc then mvc should be faster. Webforms has some overhead because of the mismatch between how things really work (eg. that http is stateless) and what is assumed while writing the code (you're programming as if the application was stateful)
In a long term which would be easier to maintain?
IMO MVC is easier to maintain, because it's easier to change bare html/js code, the model(MVC) is well defined which makes it less painful for a new person to get to figure out how everything works.
I'll need to build an admin panel to create/delete/edit pages; add/remove pictures to portfolio gallery.
This is the kind of thing that MVC is good with - define entities and quickly create List/Details/Create/Edit/Delete actions and views.
PS> I'm not saying that plain old ASP.NET Webforms is bad, it's just that it sometimes becomes too complicated and you need to pay the price for it. I think that open source e-commerce solution - NopCommerce is a good example. It's well designed, well written, but it's really slow because of the overhead that is needed for web forms.
