I have the Active Winter Rider boots and love them. I got them in a 7R and they're perfect for my 14.5" calves. I have rather narrow feet so I have some extra room in the foot bed but I think that works out perfectly considering I like to be able to wiggle my toes around in my boots especially in the winter. They are warm enough to not need super thick socks or anything like that and I found that they broke in quickly without a lot of stiffness issues. The profile is also not so bulky that you'd need to worry about fitting in your regular stirrup irons, etc. if you're seriously riding in cold weather, i'd recommend these.
I have the M.H Rimfrost boots, I have 2 pairs actually and I wear them thoroughly throughout the winters. I've had them for about 5 years I believe.
I love them. They are very comfortable and I ride all winter. I do the Jumper Series, lessons and I fox hunt in them. My feet are ALWAYS warm. I love my boots, and they've held strong for quite some time.
Just an update... I went to Dover last week when they got all those boots in. So... I tried Rimfrost, Ice Rider, and something else by Mt Horse more pricey. Ended up with Ice Rider (other two felt quite bad on my ankle bones). Will see how it'll do in winter!