Relative to the people I ride with I'm definitely better in the hills for a few different reasons.

1) - flats bore me pretty quickly. Nothing worse to me than a 10 mile stretch of road without a curve or rolling hill. I can keep pace with the peloton no problem, but man I hate those long hard slogs. Throw in some wind and I don't enjoy myself at all.

2) - when I see a hill I want to be the first person to the top. It doesn't matter if its a known sprint point or not, I want to get up it as fast as possible.

2) - on group rides people tend to remember who is always putting in good efforts on the hills. Making sprint attempts for county lines is great and all, but usually 75% of the people I ride with are all sprinting. Nowhere near as many people have the desire to push themselves past an easy spin up any given hill.

So I'm better in the hills for sure, and its all because of my mental approach and how I view them. I see them as a challenge that, when I give my best efforts, over time I will become a much stronger cyclist. I don't have that sort of mentality in the flats.