I personally think it is a good idea to at least wait until the first one has some training under it's belt...um, collar... you know what I mean.

It can be very difficult to try to get anything accomplished with two puppies, when one is a little more mature and obedient you can spend some time with the new puppy and train him/her and the older dog can also (hopefully) help by teaching things by example like going out to potty and such. The ideal way to go IS male and female, then male/male, the last female/female. There are ALWAYS exceptions, but better to be careful rather than sorry in the end. A lot of times (as you will read if you do some searches about females fighting) the aggression doesn't start until both are mature and then they can (and many times will) fight to the death. I have only ever had two males together and they did very well, and like I said there are exceptions, but there are also a lot of sad stories here about two females together, so definitely just do your research before making a decision. Best of luck! Two boxers are lots of fun!