The best split will depend on the individual. Different methods need to be implemented to determine which split your body responds best too.
The best split to hit muscles twice a week is a PUSH/PULL/LEGS split. If you recover well, use this split. This is also a preferred split for beginners.
To hit muscles once a week, your split could be chest/back/arms/legs/shoulders or any variation. If you recover poorly, use this split.
A FULL BODY SPLIT can be used 3-4 times a week, and will also result in muscle gains.
Related Questions:
The Beginners Hypertrophy Program, a program by Daniel Meyer