GLBasic is a very simple language with tons of features.
On it's features page, it lists the following as supported devices:
It can do 2D and 3D, plus supports many other platforms and devices.
They have a free version that you can check out, and when you're ready to test on those devices you can purchase the premium version for fairly cheap.
Hmm, I don't know why this got down-voted?
It is a valid answer, it just doesn't allow Nintendo devices, which most don't, and the OP did state it could be for the GPxx devices, which this does.
GLBasic allows most other platforms and since your main concern is 'ease of development' let me just say that it doesn't get any easier than with this SDK.
Using BASIC for it's base language, you can get results quickly.
It has most features that you may need, especially if you are new to game programming.
One limitation is that it doesn't have a native physics engine, but there is a Box2D wrapper in the forums.
Any questions are usually answered quickly in the forums, and most by the developer himself.
Bug fixes are quickly resolved and updates are frequent.
I realize my answer was about how easy GLBasic is to program, and not specifically how easy the listed devices are to develop for. Maybe I should have worded it to say the GPxx devices are easy to develop for since SDKs such as GLBasic exist, which allow you to program your game using a simple language, then compile and deploy to your devices with a few clicks.