Visually, Ubuntu is very distinctive and elegant. Windows has a flat, over-simplified visual style and iOS has very glossy, skeumorphic, photo-realistic icons. Ubuntu features a sophisticated, neat but natural interface that showcases your content.
While both Ubuntu and Android use the Linux kernel, and so share drivers and low-level services, Ubuntu is a full PC operating system. Ubuntu offers a more complete platform in part because they enter the market now, when phone CPUs can run a complete desktop environment remarkably well. Android was initially introduced on older CPUs and thus has many limitations compared to the full Ubuntu range of capabilities. Ubuntu apps can use all cores of the CPU and the full native OpenGL and GLES of the GPU. Being an open OS, Ubuntu is more likely to appeal to manufacturers that are already shipping Android phones than Windows.