Actually, it's been proved before that your sun sign is not even relavent in elemental magick, but rather your personality.
People best suited for water are usually quite dramatic, and at times overly emotional.
People best suited for fire are enthusiastic, and courageous.
People best suited for air are logical thinkers, and overall are quite intellectual beings.
And last but not least, people best suited for earthn have a patient, and strong personality.
I hope this aids you in deciding on your first element. :)