Dallas is closer to El Paso than Denver is.
Dallas saves ~50 miles / 1 hour of driving.
Both routes are straight interstate shots. Dallas route stays lower elevation; Denver route crosses Raton Pass (7,834 ft) and can have winter weather delays.
Dallas (DFW) → El Paso (ELP): 1h 45m, many flights.
Denver (DEN) → El Paso (ELP): 1h 50m, fewer flights.