Cold stone IS definitely pricier but it's also worth it, imo. I don't really care for dairy queen much at all, they've just never impressed me. My son is a fan, so we'll go every now and then but my husband and I really prefer coldstone.
I love both Dairy Queen and Coldstone! The ice cream is so fattening though, it is really a special treat to get something from either. Around here self-serve frozen yogurt places have been popping up everywhere and I am so excited about it. It is far less fattening and has less sugar than ice cream and you can choose your own healthy topping such as walnuts, chia seeds, and fruits. They are all a little overpriced for what you get, but for my money I would rather have a healthier froyo than a Blizzard.
If you are interested in "high" quality ice cream, then go to ColdStone because in my opinion, there ice cream is always top notch and VERY affordable for they quality they serve. But if you are more interested in just ice cream, then go to Dairy Queen!
I have only ate at Coldstone once, mainly because they aren't as convenient as Dairy Queen. There isn't a Coldstone anywhere near where I live now, so I'd have to say Dairy Queen is my favorite just because it is accessible. I found Coldstone's take interesting and think they have a nice business, however.