Rikki-tikki-tavi is similar to Nag and Nagaina in many ways. All three animals occupy the same territory around the bungalow and are dedicated to their families. Nag and Nagiana are concerned about the well-being of their eggs, while Rikki protects his adopted human family throughout the story. All three animals could be considered violent in their own way and use their natural abilities to defend themselves in battle. Also, Rikki and the cobras fight to occupy the same position at the top of the food chain in their territory. Despite their many similarities, Rikki has a dramatically different personality than Nag and Nagaina. Nag and Nagaina are malevolent creatures, who attempt to harm the defenseless humans living in the bungalow. Nag also displays his wicked personality at the beginning of the story by eating Darzee's fallen baby. In contrast, Rikki is an energetic, sympathetic creature who does not seek to unjustly harm others. He is a friend of the family and does not bother the other animals living around the bungalow. Throughout the short story, Rikki is the protagonist, and the cobras are his nemeses.

I'll start with the comparison, because I think that objective is a bit harder to accomplish.  Rikki is the hero, and the cobras are the "bad guys," so it's a bit tougher to show how they are alike.  I would say the biggest similarity is that both Rikki and the snakes care for their respective families.  Rikki obviously is ready, willing, and able to protect his human adoptive family from snakes.  That's clear right from the beginning.  Nagaina cares equally for her family as well.  That's clear when she gives up her attempt to kill young Teddy in order to take her egg back to the protected den.  

The main difference between Rikki and the snakes is in their use of violence.  Both Rikki and snakes are no strangers to violence, but Rikki uses it for self defense and the defense of weaker innocents (the humans).  The snakes on the other hand are malicious with their violence.  It's offensive in nature, and their main motivation is to cause hurt and pain for the sake of hurt and pain.  It's classic Joker vs. Batman.