There are different ways to get better on hills; personally, I am a spinner. I use the easiest gear possible on really hard climbs. I never stand, it feels awkward and my speed decreases significantly. So, I may be slow, but, I can get up almost anything, up to a 15% grade for a bit. While doing intervals in a hard gear while climbing will increase your endurance, it will also put a lot of stress on your knees. If I knew I had to do sustained climbs above an average grade of 5%, for like 5-10 miles, I might have to do more of that, but around here, it's more short, steep climbs, punctuated by descents, flats, or at least climbs that are a bit easier. The thing is, it's pretty hard to ride around here, without climbing, so I get the benefit of that, even if I am going out for a short, recreational ride. Heck, my driveway at my last home was a 13% grade for a few feet.