Wakeboarding and water skiing are very similar as they both entail you getting pulled by a motorboat across the water. However, when you get on awakeboard you will realize that it is much different than when you hop on water skis.
Overall, few people will disagree that wakeboarding is much more challenging. Before you jump to the big leagues, you should be able to handle water skiing first. From there, wakeboarding will be much easier to learn.