Classy, welcome to the forum first and foremost
I wanted to commend you for looking at performance lines in search of a halter horse and you have found some very nice stock to choose from, I can understand why you would be torn between these 3. They all look very nice.
There is something about Gwen that really draws me to her, if she grows up to look anything like her brother, she'll be a heck of a looker.
Also, with whichever one that you choose, when to geld is entirely a personal decision. There is some research that says gelding later makes the horse stay shorter and stockier and gelding earlier makes them grow taller but I don't know how much truth there is to that. If you do leave it a stud, though, just make sure that you have the proper facilities to house a stallion (even a young one).