A Soft Locker is part of the Detroit Locker name, usually seen as Detroit Soft Locker. Sometime 10-15 years ago, Eaton did something to make the locking action not as severe, hence the Soft Locker.
Luchbox Locker- One of the automatic locking lockers that replaces the spider gears in an open (and sometimes limited slip) differential case. Powertrax No Slip, Aussie, LockRite, etc.
Full case locker- An automatic locker that replaces the whole differential case. Detroit Locker, Grizzly Locker, etc.
Selectable Locker- A locker that replaces the whole differential case. These lock the 2 axle shafts together giving full traction to both tires when activated by, electricity, cable, air, or a combo of the 3 (The electric OX locker for one). When not actuated, it acts as an open differential. There are variations like the Rubicon D44, which are limited slips, but are fully locked when actuated. Ox Locker, Eaton E-Locker, ARB Air Locker, etc.
Limited slip- A traction aiding device that sends power to the other wheel when one wheel starts to slip. They work by using clutch packs, cones, or gears.
I took the D35 out of my Cherokee and put it under an Eagle. It was 3.55 with limited slip. The Eagle has a 5 speed and 30X9.5's. You can get just about any type of locker for the D35. If it fits in the D35, it'll fit in the AM15.
For snow driving, I would prefer a selectable locker. Keep it open while driving down the road on ice/snow, and lock it when it gets deep. Next choice would be a limited slip.