I have also applied to both USC and UCLA (also in the systems side) and have been trying to compare the two schools, so here are some of my thoughts:
USC does have a great reputation, especially for communication. The entire engineering school is named for PhD graduate Andrew Viterbi, famous (and rich) for inventing Viterbi Decoding. As a result, many USC grads go to Qualcomm and other telecom companies in Southern California. Graduate placement (whether in academia or industry) is highly dependent on faculty relationships, so it helps to have professors who have many connections. You should ask your potential advisers where their past graduates have gone.
USC has a fairly large EE department, which should be fine if as long as you get the attention you need from your adviser. You should find out how many other PhD students would be in the research group. A professor at a smaller university on the East Coast indicated how one might get lost in the midst of such a large program.
Another complaint I have heard about USC is that they dumb down their classes to cater to the many working MS students. Lots of companies in LA (especially aerospace companies) have employees in part-time Masters programs (which brings in a lot of money for the school), which I have heard can lead to lower course quality. This is coming from people who did not go to USC, though (and may have been jealous?).