Why can't the "N900" be it? You don't like the UI, change it. If you'd prefer LXDE, KDE, WindowMaker, FluxBox, install it over the top. Nokia have committed to differentiating themselves at the "upper" levels of the stack, and opening as much as possible of the lower levels.
Personally, I'm confident that Maemo 5 (incl. the next generation of Hildon) will be the best UI available for my use cases. YMMV.[/