few thing i can comment about Boxer:

1. they are active, very active. needs loads of area for them to spend the energy.
2. they love to bite stuff, even as adult. obedient training classes will improve but only with less frequency
3. they can be quite rough when you play with them, esp using the front leg. hence the name Boxer
4. they drool, esp when they spotted food

other than that, they are quite fun pet to have.

currently i keep a Boxer, a Silky Terrier and a Mongrel.

before this i had kept Miniature Schnauzer, Shih Tzu, Mini. Pinscher , Dalmatian

and experienced with many more dog breed

better not let them play with kids unless under adult supervision, it's a big breed after all, it might hurt the children when they goes into "Boxing" mode.

dalmatian are ok, playful and active, but mine needs a lot of outdoor activity with her or she will spend her energy on something else like destroying my stuff.

German shepherd make good guarding dog esp after training but very prone to disease when old. Doberman is just another Boxer that don't drool, Lab is the short-hair version of Retriever, and all though both are very good companion, i don't think they make good guard god because of they are so cute that i wouldn't have a slightest fear if i were the criminal

GSD (German Shepherd) /Boxer/Doberman is all good choice. However if u do not have much time to spend on them (taking care of them), i would suggest go for Boxer or Doberman as this 2 breed got much shorter hair and thus safe your time when bathing for them.

in my opinion, intelligent wise is GSD the best, easy to train, Boxer and Doberman need a little more patient and time.

rest assured, all the 3 breed is very alert.

i can't comment much on their temper, all dog i kept never ever bit me except towards stranger (people they do not see frequently)

it is difficult to tell which breed is perfect for your family, if you have children, i would say all large breed dog is not suitable but still i see some well trained large breed come along well with children. the key point is you need to send them to training, obedient training class to be exact.

i know there is 2 places, one in Ampang and another one in Kajang, or u can just drop by any pet store and ask for the training, i am sure they do have contact for those services.