It sort of depends on the house you are putting them on. Some houses look better with more variation in the shingles and some houses don't. For example, we live in a house from 1925 that has a slightly wavy roof. We reroofed last summer and chose a contrasty shingle because it helped to hide the waviness, and it worked very well. That said, we don't have any large uninterrupted expanses of roof that can look a bit strange to some with very contrasty shingles.
In the end it comes down to aesthetic preference. If you like the contrasty look, go for it. If you don't, then don't.