Younger children find it easier to draw on an upright surface due to the grip they are learning to use - this is why parents are often driven mad by children drawing on walls rather than paper provided!! So, at that age I would definitely go with an easel. You can find some lovely ones that have a blackboard on one side and a magnetic whiteboard on the other, so no matter what your child decides to use he/she will have space to do so with or without paper.
Not sure where to get them from, though, sorry. Hopefully someone else will be along in a moment with more advice!