Are there specific differences between Dartmoor and Exmoor?
Landscape is similar, also Bodmin Moor in Cornwall. I think you will have to look at other priorities rather than landscape to make your decision. Dartmoor probably has the best historical features with roundhouses and various granite man-made formations. Just to warn you, all the Moors are very bleak and cold in winter, and all the Westcountry snow falls on them. Gritting is a hit and miss process. It’s nice to look at the Moors, but you wouldn’t want to be there in winter!