TJ and Davaris are mainly the X receivers on the wide side. Starting is not really relevant because the snap count in a game is going to be pretty similar between the two. For example, Alex Welch "started" with Eifert in a double tight end situation, but on the second play Koyack was in for Welch.
A lot depends on specific packages or comfort level of coaches in certain packages, understanding coverages, adjusting to audibles — and blocking downfield. For the 1988 national champs, Ricky Watters and Pat Eilers were nearly 50-50 at flanker even though Watters had far more star power. But in that offense, you had also better be a proficient blocker, and Eilers excelled.
T.J. Jones