For actual "paint" I use Roundhouse "Old Silver". However, as metalized finishes go, I use Alclad. Their polished aluminum gives a polish no paint can match.
Expanding the question, it depends a little on the aluminum surface you are trying to duplicate. Weathered aluminum looks far different than aluminum kept buffed and polished. And there are conversion/surface treatments that look different than either. Also, some aluminum alloys left bare look different than others. Sometimes a combination of paints and metalizers are best for large planes that have several types of metal showing.