My completely unprofessional, non breeder, not very experienced handler opinion: if they are all fairly nice dogs structure wise, then go with the one that cooperates most willingly.
As a complete novice at handling, I am fortunate that Callie will pretty much stay in whatever position I stack her in. She doesn't fight me. At the same time, however, she is fairly lifeless in the ring as she doesn't get excited about much. So if I can stack her well (which depends on me doing a great job that day), she will stay there & maintain that position, but then the challenge is to get her to stop looking so bored. I've taken other dogs in the ring that refuse to let me touch them, refuse to be stacked, etc. So for me, just for learning the ropes, Callie is nice because I don't have to worry about her fighting me, just getting her looking alert.
I'm sure somebody might disagree with my opinion, and like I said, I don't have much experience to offer or opinion on which dog to choose structurally. I just like having a dog that isn't difficult to stack.