Well, a very long time ago (January) i showed interest in developing a game for N900. I still have, however i have a difficult time choosing the right graphics engine. I am certain that i want to use one based on Ogre, as its good and free.
However, i dont know which variant i should pick. There is the normal one in C++, PyOgre and QtOgre.
Now, out of these, i would like to have a simple one. That makes me think of PyOgre. However, i dont know how it will be to port it, and in that case Qt one is better. But again, i am wondering about the Qt version: will i be able to directly use the desktop version on N900 through Qt?
I read somewhere that in Qt, it doesnt matter if the app is written for OpenGL, as it will work for ES as well because of the Qt-layer.
Another thing is that the normal Ogre might have better performance, but it would need to be ported in order to work.

Which is the best to go for?
I need a 3D engine that can both do good performance and has many graphical effects available.

I work as a day job for the www.realxtend.org project. We are making an open source 3D virtual worlds viewer. We use lots of deps and our 3D engine is Ogre. I have successfully cross compiled ogre 1.7 and the 1.8.unstable (the hg head at the time) for maemo 5/N900. Ogre is working nicely with GLES rendering system, I have build GLES2 rendering system also successfully but ogre refuses to load it on the N900.

Our projects main framework is Qt. We have ogre rendering into a window handle of a QWidget. We disable paint events and manually on our own main loop render Qt into a ogre overlay texture. This way we don't get flicker when two systems are competing to paint on the same surface. Qt is not using OpenGL but the raster engine as it does not do any heavy painting, that is left for ogre.

http://www.youtube.com/watch?v=IP7zty5Kg7g Check out the video, at least you know this is possible!

I haven't packaged our client, ogre, poco or any of the other numerous deps we have. It was demo kind of thing I just did to prove it can be done with the N900 in my company

For the Qt code. You can use Qt 4.6.2 on the OS you develop and it should run fine on the device after you cross compile your code, can be done in QtCreator >= 2.0 or in scratchbox as I did.

The N900 client looks pretty cool. Good work! It is a pity that GLES2 is having some trouble, though...