How comfortably should hiking boots fit?

if i had to choose, i'd probably say a larger boot is easier to deal with. your toes will really start hurting in a too-small boot and there would be nothing you can do about it. although i once did some long-distance hiking with a too-big boot and my blister problems were terrible. lost a couple toenails, too. but like has been mentioned, wear double socks, and an insole (I recommend SofSole) will also help to fill the space. be prepared for blisters, regardless. and double socks can exacerbate that problem through making the foot hotter.

I would say better too loose than too tight. You can always add extra layers of socks. That's what I do. I wear an 8.5 size shoe, but due to the shape of my foot, the only boot that fit me comfortably was a size 10 (granted, there could be some differences in the sizings, considering different brands, etc.). I usually wear 2 pairs of socks (a thin pair and a thick pair) and my feet are perfectly happy!

In my opinion, you should find a size that fits really nice and comfortable in the store... and then go a half size up. Your feet will swell on the trail, or you might want an extra pair of socks, at some point. I like my boots loose. I bought some that seemed right in the store, but after a few hours of hiking, my feet swelled and I wasn't very happy at all. Tighter boots actually give you more blisters than looser boots because there's more friction involved.

It is better to have boots that are a little bit too loose. That way if you need to fill some extra space, then use some extra socks, and that should help!

Your feet do swell on the trail.