USAA, as you probably know, exclusively serves active-duty military, veterans, and their families. They also offer special discounts such as 60% off for vehicle storage and discounts for taking a vehicle overseas.
GEICO offers 15% off of premiums for military members. They also have veterans on staff who understand and can help with any insurance situation you may encounter as a military member.
Depending on the type of coverage you need, you may find one company is better for you and your needs. That said, you should request quotes from both companies to see your rates.