This sounds like an essay question. In my experience as long as you can justify your answer and explain it well, it won't matter which side you choose.
I would say it's internal conflict. Tris is trying to figure out if she feels loyal to Abnegation. When she chooses Dauntless, she spends a lot of time comparing herself to the Dauntless born initiates. She doesn't feel strong enough or as adventurous as the others and is constantly trying to search herself to find out where the Dauntless in her is. At the same time she feels disloyal to her parents for choosing Dauntless instead of staying in Abnegation. She spends a lot of it time wondering if she made the right decision and feeling like she betrayed her parents. It's a battle between what she wants and the selfless attitude she has been brought up to believe. That's the internal conflict.
The conflict could be described as man vs society. Tris starts as a character who has been trying to act selflessly for years. Her character develops so much throughout the book that at the end she is more determined to fight society and the faction system rather than play along like everyone else.
