Answering the question who is most compatible with a Sagittarius, according to Zodiac Sign Compatibility chart there are two signs: Aries and Leo.
Leo and Sagittarius is a successful couple of strong, creative, free persons. They both like to travel and search for adventures, great sex partners. Their life is cheerful, they accept adequate level of risk and do not make fully mistakes. They are same minded and this leads to success in relationship.
Aries and Sagittarius are good friends and passionate lovers. In this couple Aries shows initiative, Sagittarius in his turns helps Aries grow and develop. Both signs being independent allow each other to feel certain level of freedom without hurting each other.