For me...Brooks Robinson was the greatest fielding 3rd baseman of all time...and I "stole" his nickname for myself at yankee fantasy camp as I was the best fielding 3rd baseman there!!!!!!
Growing up a yankees fan...I followed George Brett's career more closely than Schmidt's...as he was more a direct adversary...and I had a love hate relationship with him...as I had infinite respect for him...but hated when he played well against the yankees.
In light of this...I feel Schmidt is the greatest 3rd baseman of all time.