Hmoll is right.
Physically the most difficult key to play is C major, closely followed by the spare accidental ones, G major, F major, Bb major and D major. As the accidentals increase so does the facility with the easiest keys being the ones with most accidentals: B major, Gb major, and Db major. The reason is simple: they conform very well to the anatomy of the hand: the long fingers (234) play the black keys, the short fingers (15) play the white keys.
Most people freak out when they see heavy key signatures, but actually this is a problem only if you do not know your scales well, or if you follow the common teaching approach of learning C major first, then G major and so on and so forth. If you start learning scales with B major, Gb major, and Db major, and proceed from there by subtracting a sharp/flat, soon you will be so conversant with these scales that there should be no problem in either memorising/recognising black key pattern, or sight-reading through them.
Best wishes,
Bernhard.