Headwinds v Hills? Maybe it's a different view from where I live, but I would love some nice tall hills right outside my door.

The one good thing about hills is that they are reliable. They have a top and if you are doing an out-and-back or a circuit back to the same start point, you'll have as much decline as you'll have incline.

Headwinds are very unreliable. Start the ride with a slight tailwind and you'll feel like you're in for a great ride, but once you head back into the wind, the day changes. And if that wind picks up, it's time for suffer-fest. You can't see what's holding you back, whereas with (most) hills, you can visibly get an idea of how much farther or harder the workout will be.

Now... combine the two and you got yourself a whole new set of circumstances...

Keep on climbing!!!