There is basically no nvidia drivers available for many modern mobile GPUs on Linux, so I doubt that Nvidia is more linux friendly than ATI/AMD nowadays.
AMD is ruthless about dropping support for older architectures, which hits laptop GPUs especially hard. They're about to drop support for R600 and there's still lower-end devices being sold with those. Fortunately as noted above the AMD open source driver is pretty good, more than good enough for a laptop I would think.