it does depend on the terrain and such... I run mostly at Rausch Creek (east coast rock trails), with a little bit of mud in New Jersey. I noticed a huge increase in traction after doing a longarm, I rarely lost traction because the front end flexed so well and kept the tires on the ground more. I was able to run much harder lines than normal. Many of the harder spots at Rausch Creek are going up hills with boulders scattered along it you have to get over, so the front does most of the work.
With that in mind, I can only imagine what it'll do with a locker. My only issues were when I'd jam one of the front tires against a rock. With a locker, it would pull over it, but since it's unlocked, the other tire would get all the power and just spin. Never had that issue when the rear tires hit it, since the front axle would pull the rear up and over.
I picked up a HP30 with a trutrac, that should be tame enough for snow, and be strong enough for the trails. (with riding the brake occasionally to keep it locked). I'm currently slowing saving money for a rear ARB and gears for front and rear. Once that's all set, I'll install the HP30 and have somebody set up the gears and install the ARB for me. Selectable is the way to go for the rear, at least if you daily drive it and drive in snow. I'd do an ARB in the front, but don't think I can get anywhere near enough money out of the Trutrac to make it worth it.
That said, you're on different terrain and trails than me. If you do more hill climbs (full throttle stuff, not slow rock crawling) then a rear locker might be a better choice. Keep in mind that steering will be different with a front locker since you lose the differential action of the open diff. Baja-type stuff, definately the rear, since the weight will be shifted to the rear of the Jeep and lighten the front giving it less traction.
Good luck!