I will say this about flats, flats with a big tail wind make me feel 30yrs younger. Spin'n big gears is fun.
Now, here's a man I'd enjoy riding with. Me? I'm the oddball. I "hate" hills. We have few around here, mostly mountains. Out here in the high desert, away from the mountains, it is possible to ride the flats mile after mile without having to stop. Very easy to get into a rhythm and just motor away. That is an enjoyable ride to me. More so with the afternoon prevailing wind with me.
I think I learned my dislike for hills when I went on my cross-country trip. I made a major mistake and went from east to west along the southern tier durning the springtime. Going over the Appalachians was one of the most discouraging things I have ever done in my life. The bke was fully loaded with everything I needed for a self-sustained cross-country ride; panniers front and back, rack packs on top of that with the sleeping bag and tent. Carrying quite a bit of weight, it was a struggle going up the hills. Thinking to myself, "at least I can coast down the other side". Oh no! When I got to the top of the hill and started down the other side, the wind was in my face and I had to pedal downhill to maintain any type of momentum. Only at the very bottom of the hill, in the wind shadow, was the air calm. But, after a very brief interlude, I had to huff it up the next hill. Hill after hill . . . day after day . . . no wonder I don't enjoy hills.
I still ride them. Mostly because "they" say it will make me stronger. Hah! Hasn't happened yet, but I will still struggle away at them.