It depends which direction you want to rotate around the axis. One will rotate it clockwise, the other anti-clockwise. This is because Sin(-a) = -Sin(a) and Cos(-a) = Cos(a), so the 2nd matrix could be written as:

Do it as the romans do, that is use the matrix that rotates counterclockwise, which means that you use the second matrix you have provided, with a possible negative argument to sin() or cos() functions.