Even as a beginner piano or keyboard player you will notice that the key of C major is the easiest to learn. Why? because it consists of all the white keys only. This also makes it very easy to visualize how the chords are made up. For example starting at middle C, simply skip every other key to create a major chord. C, E, G – C Major would be the most basic example. Also you can see that the space between the keys are exactly the same. So does this make the C major the easier key to play? Definitely the easiest to understand and visualize but not really the easiest key to play in.
Many people would agree with me that C major is actually one of the hardest keys to actually play on the piano. The reason being is that the C major white keys do not seem to fit the contour of your fingers naturally. Personally I find the keys F minor (or Ab major) one of the easiest. F minor is the same as Ab major, however visualizing it as F minor we can start with the thumb on F. Your fingers can naturally move across the keyboard via keys F, G, Ab, Bb, C, Db, Eb. A very comfortable movement and a lot easier than C major.
Another popular key for pianists and a key I also love to use is Bb major (G minor). It seems a perfect fit for the hand and also finger movement. Also, a lot of horns and brass tend to be tuned in Bb so it would easier to play jazz with that key with other musicians.
Other keys considered quite difficult for piano and keyboard players are A and E major. These tend to be guitar chords, i.e. chords easier for guitarists to play. I also don’t feel that my fingers fall naturally into the keys positions. I have played on stage in the key of E major which was fine however I was not too confident with improvising the solo part. I made sure I fixed and practiced a solid solo in that key. Had it been another key, such as Bb major, I wouldn’t have needed to practice so much.