What dog breed should I get?

I have a big backyard and plenty of space. I'm active and I do a lot of outdoor activities. I want a semi-aggressive dog that's going to protect me against an attack of some sort, but is still patient and loving with kids. I'd prefer a dog that's going to guard my kids and protect them too. It is a multi-dog home so it would need to get along with other dogs too. We have plenty of space for a big dog. I'd like a dog that's going to want to join in the activities, but is independent as well. I live in Texas, so it's going to be hot in the summer. I know some breeds don't do well in the heat. But it also gets very cold and sometime snows. I'd like a bigger dog, simply because I've never been a fan of yappy dogs. I don't mind a dog that takes a little bit of grooming. Bathing and brushing are okay, but I don't want to have to give it a bath every two days. We also have horses and cattle. I want a dog that can do shutzund(protection), agility and obedience. There are several dogs I'm interested in, but I just don't know which. I am an experienced dog owner and I've worked with many breeds, so a headstrong dog isn't a big issue. Here are a few to think about:AkitaAlapaha Blue Blood BulldogAmerican Pit Bull terrierAregentine DogoAustralian Shepherd, standard or miniatureBernese Mountain DogBoxerCane CorsoGerman ShepherdRottweilerPlease no bashing the Pit Bull terrier. I already own one and part of me would like to get another.My kids are 1 year old and 5 years old. I understand some don't feel some of these breeds are okay with kids, but I disagree. Please don't list any breeds not on this list. I have them listed because I had it narrowed down to those breeds and I probably don't like the way those other breeds look. They're simply not my kind of dog.