Thanks for all of the input! As I suspected, both breeds--boxers and am bulldogs--are great breeds, and both possess the qualities I am looking for: large, athletic, loyal, protective but friendly, and intelligent. I think I'll have to check out some local breeders and spend some time with adults of both breeds and then hopefully I can make up my mind. Luckily, I don't think I can make a wrong choice with these two breeds.
Jade, your two Johnson amdgs are awesome! Did you get them from the same litter? I also looked up some pics of Body 88's dog and was super impressed.