User blog comment:JWarrior89/Lord Voldemort vs Darth Vader (Rematch)/@comment-2006360-20120210155317

Voldemort is smart. When Nagini was his last Horcrux (at least so he believed), he kept her under protective spells. He will only use Nagini against Vader if he has no other option. He also has a wider arsenal of magic (so to speak) abilities than Vader and his Death Eaters are stronger than Stormtroopers.