On offense, I'll go with Marlon Mack. Gore could really start to wear down by mid season and then it could be time for Mack to shine. Mack is a 3rd round back who went in the 4th round, and has very good agility in the open field and could be a great check down option for Luck.
On defense, I'll go with Henry Anderson. He started showing signs of being a really good player in 2015, until his injury. From what I'm hearing, he should be hopefully 100% and that could allow him to really break out this year, especially with Hankins taking some pressure and added blockers off of him.