Aires might be switching stalls at the stable because one of the other boarders is getting another horse and they want their two horses to be stalled next to each other so that they can get used to each other. Fine, I'm that picky.
However, my friend and I were walking around the property this afternoon and realized that there is a huge end stall that is 85% shaded down by the arena that is open. I like it because it is away from the road (Aires' current stall is right next to the road), he'd get used to the activity in the arena (a must of we're going to be doing any kind of showing), and hopefully it'll get him used to stuff going on all around him so he won't be so "OMG! I'm going to die!" about his right side (right now he stands with his left side to the road and nothing really on his right, so he's extremely flinchy and scared about his right).
Anyway, the downside of this prime piece of real estate is that it happens to be the wettest stall on the property. All the other stalls are slightly uphill from this stall and so everything drains down into it. This would be a significant problem if we lived in somewhere like, say, Washington state, where it rains all the time, but we live in Northern Arizona, where we have monsoons for about a month and a half and where it rains a bit in winter, but nothing spectacular (we had snow twice, maybe three times, this past winter and that was considered a wet winter...but we never get more than a few inches).
So, what would you do? Keep him in the smaller stall (about 30ft by 20ft) that is drier (the stall he'd be moving to is the same size as the one he's in now)? Or move him to the bigger stall (probably 50ft by 30ft) that has more shade, but is wetter?