What will you use for iPhone development?

If you include Flash there are now basically four platforms you can use to build native applications on the iPhone. Firstly there is the traditional Cocoa touch and Objective-C route, this is the best supported, documented and mature of the three. Even if you don't know Objective-C, the language is fairly easy to learn if you already know a C-derived language and have a basic grasp of object-oriented programming. If you want to develop seriously for the iPhone platform I'd recommend getting as close to the metal as you can and using the official SDK.

However there are alternatives...

Monotouch from Novell which allows you to build C# and .NET based applications on the iPhone and iPod touch. It comes in two editions: Professional and Enterprise. A license for the Professional Edition, intended for individual use, costs $399 per year. While the Enterprise Edition, intended for corporate use, costs $999 per year (although you can buy a 5 developer pack for $3,999 per year). Alternatively you can download an evaluation version that enables development and testing against the iPhone simulator only. I've played with MonoTouch fairly extensively and I've not found it to be particularly stable, especially when using the MonoDevelop development environment.

Then there is PhoneGap, it's an open source development platform for building cross-platform mobile applications with Javascript developed by Nitobi. On the iPhone it works by providing a pre-built Xcode project containing Objective-C classes that wrap the iPhone’s native capabilities (e.g. geo-location, vibration, and accelerometer support) and exposes these capabilities to Javascript. You can then compile your application as a hybrid of native Objective-C and Javascript inside Xcode.

The PhoneGap platform is device agnostic, allowing you to build an application for the iPhone, Android, and Blackberry devices simultaneously. If you've got a lot of Javascript development experience, building applications using the PhoneGap framework is a reasonable alternative to building all native applications in Objective-C. It certainly seems to be a lot more stable than MonoTouch.

Finally the Flash development environment. It's not yet in general release, so I admittedly haven't played with it, but I'm going to be surprised if it's not a bit on the buggy side at least at the start. MonoTouch has been around a few months now and it's still pretty buggy.

Thanks for you comments, Alasdair. I wasn't aware of the other environments available for iPhone dev.

There's also Unity3D, which will build an XCode project for you. It supports javascript, C#, and a dialect of Python called Boo.

While Unity 3D can now produce iPhone builds, it's a multiplatform game-development tool, rather than a general purpose development platform.