191 is a very scenic drive and a good road. There is one bad section that you will have to slow way down as it's very rough road. Still pretty, but rough. That's between Royal and Duchesne. If I didn't say it before, slow down on this section. The rest of the road from Moab to Rock Springs is wonderful.
You can stop at Vernal UT and see Dionsaur Nat. Mon and going further north stay a day at Flaming Gorge.
Mid April in the higher elevations you will have some snow on the ground, but the roads should be clear.