WPF is all the rage (at least that's what they tell me) and it's IMHO one of the best technologies to come out of Microsoft. Still, however, companies choose to stay the course with building on WinForms. Karl Shifflett has a great blog entry on choosing WPF over ASP.NET (and great entries on WPF in general so check his blog out here). To me it's a no-brainer choosing WPF over ASP.NET, unless you're really enamored with a browser app (or forced to build one due to some constraints) and with Silverlight and XBAP (and the new features coming out shortly in Silverlight 2) building a rich interface for the web gets better and better. AJAX just doesn't cut it and is a hack IMHO.
Making the decision between WPF and WinForms however is a different story. Sure, WPF is the new hotness and WinForms is old and busted but is it the right choice? Obviously "it depends" on the situation and Microsoft is continuing to deliver and support WinForms so it won't be going away anytime soon. So what are the compelling factors to choose WPF over WinForms? Karl hints at choices of WPF over WinForms in his WPF Business Application series, but the reasons might be subtle for some.
If you're struggling here are some reasons for choosing WPF over WinForms, and let's play devils advocate as you might have to fight for some of these.
Why start new development on old technologies? There's bleeding edge (Silverlight 2 perhaps) and then there's cutting edge (WPF?) and we can probably start to talk about WinForms as legacy. Start, not come to that conclusion. WinForms development can be painful (much like moose bites) but the latest technology debate is a tough one. One on hand it's lickety-split to create WPF using the tools available today (see below) and from a development perspective WPF shines because everything is an object. The crazy hoops you have to jump through just to get an image on a button or menu are all but gone when you try embedding an object onto another one in XAML. On the flipside though, most of the large UI suites (DevExpress, Infragistics, Component One, Telerik) haven't fully completed their WPF implementations and the maturity lies in their WinForm incantations. Still, starting a new project today that might be delivered say 6-12 months from now doesn't make a lot of sense building on what some might consider legacy but as usual, you have to pick the right tool for the right job.
While WPF is pretty young in the eyes of consumers, Microsoft has invested 5+ years of development in it. WinForms arguably has the edge on maturity here (existing since the .NET 1.0 days) but don't knock WPF as a babe in the woods. It popped up on the R&D radar back in shortly after .NET 1.1 and Visual Studio 2003 came out and has been gestating ever since. This is a plus point if you're in a boardroom or meeting with some stuffies who think it's new and shiny but with no meat behind it. Combined with its own set of unique features, try something like UI automation and WinForms and we'll talk maturity. 10 years after WinForms was born and we're still struggling with UI automation. WPF solves this in one fell swoop, and does a nice job of it to boot.
While we live in a domain driven design world (at least some of us do, you have come out of your cave right?) with objects and collections and tests oh my, there is still the UI to design. I'm not a huge fan of the move to CSS validated Expression Web, but I understand (and agree with) the choices Microsoft made with the model. Kicking it up a notch and delivering Expression Blend with it's integration into Visual Studio makes building WPF apps a breeze. In fact, I strongly advocate and support handing the UI design off to someone better suited to it. Let's face it, developers suck the big one at building UIs (unless it's "Hello World" with a big button and an image of Scott Hanselmans face on it) so let's let the UI designers design. Blend lets you do this by just letting the designers "go wild" as it were, without having to worry about "how in the heck am I going to hook this up later". Giving a designer a copy of Visual Studio to design a WinForm app is just plain crazy, and don't even try to convert their JPG mockups that have been signed off on into a Windows Form (been there, more t-shirts, I have a lot of them) but getting a XAML file from them just plugs right into our development environment and is dead simple to wire up to whatever back-end you have going at the time.
How many bugs do you have logged on your current project that say something like "cannot see button x when my screen resolution is 800x600"? As a developer, we generally work at crazy resolutions that no sane person would run at (my current desktop runs at 1680x1050) so building forms on this just plain doesn't translate well (read: at all) to a users desktop of 800x600 or 1024x768. Buttons vanish, menu options disappear, and that oh so beautiful grid that is the lynchpin of your appplication is missing the bottom 20 rows and last 10 columns. Sure, WinForm containers and whatnot help but far too many times we forget about this and end up building things off in unseen areas of the screen. WPF doesn't solve this problem, but really helps. Not only that, we're not asking users to change the resolution or font size on their screen to see things clearly. In this day and age, users need to be able to dynamically change the system at will when they're working. I've seen users running with the extra large font theme as their eyes give out on them but apps just plain don't work well when your system font is 36pt Verdana. Look at the iPhone as an example of clever UI integration. It dynamically zooms in and out as you choose to make things readable. We need more of this on the desktop applications we build to suite the needs of users who want "to see it all" at once. WPF let's us do this with less pain than WinForms.
WPF allows for much easier data binding through its model and this can result in faster development time. Now Unka Bil isn't telling you to go out and bind your WPF creations directly to ADO.NET models. I still live and die by Domain Driven Design so binding happens on objects (probably best through a Binding<T> adapter of your domain classes) but WPF does make it easier to do this if that's your thang.
So overall it's a better experience, both from the development side and consumer side. Again, you might have some battles to fight with Corporate to jump onto the technology band-wagon, but this is might be a battle worth fighting for. WPF is no silver bullet (as I always harp, the is no silver bullet unless you're fighting werewolves) but hopefully this will help you make a more informed choice. The choice is yours, but choose wisely.