What is better- cable lugs with or without tin plating?

This choice is made after you understand the environment where the lugs need to be installed. If the weather conditions are relatively dry like in Kazakhstan, Siberia or Turkmenia, you can easily use copper cable lug without tin plating. If your connections should be made in moist environment-subtropical or arctic, or the atmosphere is polluted like in Moscow, it is better to use tin-plated copper cable lugs.