Trail rig: rear locker first, then later front traction device. Daily driver or more pavement than 4x4 trails, rear locker or Detroit Truetrac first, and later Detroit Truetrac front.
Unless e-lockers have improved their durability, I would not.
What will be the usage ? what is the budget ? If you really want a front locker a selectable locker is best.
If you are only going to use a traction device in one axle, put in the rear. I have done it both ways, front first and rear first, and always recommend the rear axle first. Two reasons why: The rear axle typically has the greatest weight transfer and useable traction on the 4x4 trails, and on pavement a rear locker is the most predictable. The front axle unloads weight to rear on the 4x4 trails, and front lockers in winter weather road driving conditions really suck. They have undesirable behaviors and borderline unsafe behaviors.
Somebody will always chime in that a front locker will pull you up ledges, which is true, but this is not a good enough reason to lock the front axle first. A locked rear axle will push you up nearly any ledge, and as already expalained has better manners and more opportunities to increase traction on the rest of the trail. A front axle locker scratching at dirt on the crest of an obstacle has very little weight on the tires to put the extra traction to good use.