Criteria

You may want to add or subtract from this list, but this seems to be a basic set of criteria:

• Progress through the learning process in a logical manner
  • Start with a simple manual process that teaches you
    • how to control an arc
    • how much metal filler you need
    • where to place the filler for superior weld beads
  • Add to that skill with more precise control
    • Separate the arc from the metal deposition function
    • Coordinate those functions in optimal form
    • Add versatility to enable comprehensive skill
• Ability to weld all types of metals
  • thin sheets and tubing
  • dirty or rusted metals
  • thick stock
  • high strength
  • non-ferrous metals
• Clean and attractive welds
  • Metal stock must be accurately cut
  • Metal stock must be clean and free of burrs
• Precise control
• Adaptability and simplicity of welding machine
  
  • Avoid necessity for extra attachments
  • Use same shielding gas for different metals to have just one bottle
  • Adapt machine waveform 
    • AC - useful with aluminum
    • DC - most ferrous metals
    • Duty cycle - control heating
• Ease of striking the initial arc
  • High frequency start
  • Programmed gas flow and amperage profile
  • Hot start for consumable electrodes (stick)
• Reasonably easy to learn
  • "Easy settings" for AC and DC
  • Precise control for fine tuning
  • Advanced wave forms for AC
• Modern settings for stick welding
  • Shock hazard control
  • Arc force settings
  • Hot start time and intensity settings
  • 6010 cellulose rod capability