You should also keep in mind, that at this time (11th/12th/13th of April?), easter holidays have already started in some parts of france, great britain and other countries. So the chance to get an empty park ist pretty low. It is more about which day is worse - and accroding to this and the fact, that you seem to have just one day for both parks, I would try to make it on one of the two weekdays. For me, DLRP is one of the most awful parks when it gets too crowded.