I think the horses personal care would be top of my list...
Both barns offer very close amenities actually.
If your horse is going to be on "outside" board, I would be thinking he would be uncomfortable in a "heated" barn situation. It is the horses needs being met not yours. You need to dress for the biting cold, not acclimate the horse to warmth and then back out to the cold...as long as you are out of the winds, the cold the horse can adjust for and you can put coolers or blankets on as needed before, during or after a workout.
My other thought is... attached indoor to the barn can sometimes create a dusty breathing environment, over time a breathing health issue.
I would go for the barn that is a separate indoor so the horse is not breathing that "dust" longer than necessary.
Also a "closed" up barn as such... I prefer a fresh air environment and good air exchange so respiratory problems and illnesses are harder to transfer, hopefully the barn workers are diligent in equine hygiene practices.
I also like the individual pens idea. I am not of the mindset that says they must be out in a group all the time. Fed in their respective "private" area so you know your horse ate his ration & supplements not the neighbor eating his and pushing him away or your horse eating anothers...I don't go for group feeding of grain... see to many horses learn to bolt their feed for fear of not being left to eat in peace. Individual will also allow you to know if there is a eating issue with your horse.
I would think that there would also be hay fed in a turnout that all can munch at during the day, many piles or a few round bales so no one is pushed away or chased off...
Makes no difference to me what discipline is being ridden.
Skilled riders no matter the discipline all have certain basics that are common to all... biggest thing to me is other riders having ring courtesy and respect for fellow riders.
Although one indoor is larger, it isn't by a great amount truly...and the smaller indoor is absolutely ride-able and workable in even in company...all boils down to respect for each other and ring etiquette.
Me... I would go for barn #1...
the horses needs sound better met.
Your needs are second to his, yet all is more than adequate that is provided. Are there bathroom facilities???
To me that is a must!!