Very interesting responses, thanks everyone!
Out of more curiosity - because I've had different people tell me very different things about my horse in particular - what do people think of my mare's natural headset/frame? She highly prefers to move out with her neck up and nose out like the first photo and my profile pic. Probably has to do with being 1/2 Arabian, it's just where her neck is set, I believe. If I drop my reins, she'll move exactly like that all day, it's where she's comfortable. She will collect without hesitation like in the second photo if I ask her to, but will only stay that way for 10 seconds or so before returning to her natural frame if I leave her alone. (I apologize for the poor first picture quality, it's the best I have of her moving the way she wants.)
There are people who have told me her natural movement might not display the prettiest headset or frame, but if it's where she's comfortable, it won't hurt anything, and that she will still build muscle where it matters. I have had other people tell me that they would like to see her always go like the second photo, because it will strengthen her topline, and the more she goes that way, the more she'll want to go that way.
Essentially all of my training has been with English people who want to always see every horse either collected - not high-level-dressage-style collected, but more hunter-style or very low-level-dressage collected - or stretching down. So I'm trying to see things from a different perspective after 10+ years of being spoon-fed that all horses need to go that way.
We don't show and don't have any plans on showing, so we're not trying to win any awards in the looks department. This is strictly keeping my horse's best interest and strength in mind. We do almost all of our work on the trails. Personally, I have no interest in constantly asking her to collect for months until she maybe does it on her own, so right now she's going the way she wants to go. For the sake of my horse, and not the sake of any judge's expectations or what is "correct" in any given sport, which way would you ask her to go? Is there any real benefit to collecting her if she prefers not to and we're just doing trails?