Both are as good as the other and it's important to vary any exercise routine, otherwise the body adapts and just gets used to the exercise.
I personally prefer the Cross Trainer, as there are more programmes to follow, therefore alleviating the boredom factor and you can concentrate on toning upper and lower body as well as the regular cardiovascular workout.
As someone who works in the Fitness Industry, I highly reccommend Life Fitness Cross Trainers. They are sturdy and good quality, but expensive.