I would take a grade. I can gear down and make due. The constant grade thing is a little different. With a hill there is a reward on the other side... The wind can be deafening and infuriating at the same time. My first ride in a while was simple ten miles out (downhill) then ten back (uphill). I loved averaging 20 - 25 mph. I felt like the bike at the gym was a real good substitute.... Strong head wind back. I almost had to walk. My low low only let me go @12mph with a cadence of 85. I stole the group off my similar vintage Raleigh and now I could climb walls. I can do @4 mph at 90 cadence in low low now! I no longer fear head winds while going uphill. I must now shop for a new group for the Raleigh now-
The thing about headwind is the harder you push against it the harder it pushes back. If you have a 20 mph headwind and you travel 5 mph into it then you no longer have a 20 mph headwind. You have an effective 25 mph headwind.
I just got back from a tough 5 mile out and back ride on the bike path. The winds were gusting up to 35 MPH, and all I was could think about how this ride was supposed to be an easy weekend ride (flat) and that it seemed harder than pedaling up and down the 15% grades I have near my house.
So if you had a choice, which would you choose: 30 MPH head/cross winds or constant 12-15% grade hills?
Head wind because it comes with a pleasant cooling breeze.