UDK all the way. You really won't find a better set of tools. It contains pretty much everything you need. Making maps, programming in UnrealScript, creating materials, etc. It's all a breeze and amazing.
It's also incredibly easy to fix the camera to scale horizontally (although I actually think the camera scales horizontally now by default. I need to go over the February release of UDK.)
You can use ScaleForm for the interface.
I have yet to find a better SDK. It's the complete package.
Actually I have started to like CryEngine 3 SDK more then UDK. Even by the short time I have used it I am very suprised by it. If you take a program like 3ds max and CryEngine 3 SDK those to programs are very similar in many ways. Also importing entire scenes into CryEngine 3 SDK is allot easier. You can even program objects directly inside the Engine and update what you have programmed without having to restart the hole Engine like you have to do in UDK. I just think CryEngine 3 is more user friendly.