Grand piano's and upright piano's key mechanisms are the same and therefore there will be no difference in the feel of the keys. Though one is horizontal and the other vertical, they are designed to have the same touch.
The only difference between a grand and an upright is how the strings are laid out. The upright takes the strings, that in a grand are place horizontal to the floor, and arranges then vertically so as to save space.
The difference between these two types is not in the ease of playing but rather in the sound that is created. The soundboard is the wooden piece that lays next to the strings and helps create the resonance that gives a piano its rich sound. Being place horizontally above the floor verses vertically facing either a wall or an audience can change how the piano sounds. These differences are minimized as much as possible by piano makers, but there will always be some difference between the two.