i would go for the g27, the g27 is noisy, and the wheel does lack buttons (does not effect me)
but ajustable pedals would be amazing, that alone is worth it.
the shifter is better built, and feels much more realistic, but you lose sequential.
the sequential is not that great, or even used often by me, and you can always use the paddles or even rig something up yourself to use instead, for those cars.
so i say a g27.