It depends on how you define 'easier' actually. Less algs to memo? Less time taken to solve? Less lookahead required? Less intuition required?
Whatever it is, the next step after 3x3 is always 4x4. Skipping straight to 5x5 isn't a good idea IMO, since in 4x4 you learn the basics of centre making and edge pairing. But 5x5 is easier to solve intuitively after the 3x3 though =p