Your question opens the door to as many opinions as there are people who'll answer it, right? ;)
So, here's mine: Parelli, Level 1-2, 7 Games (groundwork), Horsenalities, yet with a qualified mentor who can assist you on-site if necessary. (How close is aunt?) I add this proviso due to many PP students who've missed the boat because no mentor was there to help. (like trying to learn ballet from dvd's, with no teacher to correct).
Learning as much as you can about the bnt's via that link is of course advisable. Some are good trainers, yet aren't entertaining, btw! Some are harsher than they need be, some keep their horses' heads looking down at their feet, which you'd want to avoid, & some MAKE their horses do stuff, rather than motivate the horse to want to be with them because it's fun. I'm sure you want your mare to WANT to be your partner.
I suggest also that you ask for wisdom from Above on your choice, because horsemanship wisdom is not human speculation, opinion, fashion applied to the horse, but is wisdom/understanding that can only be given from Above.