Short Answer:  The more complicated, the more secure
Detailed Answer: 

Your WordPress password should meet the following requirements:
  • Include Numbers
  • Include Capitals
  • Include Special Characters (@, #, *, etc.)
  • Make it long (10 characters – minimum; 50 characters – ideal)
  • Cannot include spaces
  • Pro Tip: for maximum security, change passwords every 120 days (4 months)