As has been said...neither is better than the other. They're just different. Both breeds have very different temperaments and needs.
Boxers, for example, needs a
lot of exercise, whereas Rottweilers (although active) don't need anywhere near as much.
You need to be very specific when asking yourself what you want in a dog.
How much exercise (and what type of exercise) are you willing to give it?
How much grooming (that doesn't just mean brushing the coat...that includes nail clipping, teeth brushing, wrinkle cleaning etc...)?
How much socialisation and training are you willing to give it? If you get a more protective breed you need to give it a lot more training and socialisation in order to make it a good member of society.
Where will the dog live? Will it be inside most of the time, with access to a yard? Will it be an entirely indoor dog (perhaps in an apartment)? Will it live outside? Will the yard be fenced? Will you have a dog run for it instead?
How much money on vet care are you willing to devote? (some breeds are more prone to health problems than others...Boxers, for example, have a high incidence of cancer in the breed).
Write down a list of all the things you expect of your perfect dog and then try to find one that matches that list. You can't mould a dog to fit you, you have to find one that already fit in the first place.
Good luck on your search though. You may find a different breed suits you better...you never know. At the very least you'll be able to figure out if a Boxer or Rottweiler better suits you.
Cass.