Now that we've sucked you in with that title, we'll tell you right now that it's not a matter of which differential is better, it's a matter of which one is better for you!
Limited-slip differentials and locking differentials are both added to axles in an effort to achieve more traction in environments where one wheel can break traction and spin, leaving a vehicle with an open differential doing what's known as a peg-leg dance. Without having a limited-slip or locking differential in an axle, you can lose forward motion when one wheel breaks traction and spins, leaving the other one (wheel) to sit idle. Having a traction-aiding diff instead of an open diff not only helps in the dirt, but on pavement as well. In fact, we prefer something other than an open differential in any truck, SUV, or car that we drive.
It's about this time that you're probably asking yourself, "Why wouldn't I completely lock both axles together full time with a spool or something?" And this is an excellent question. A spool is a simplistic, one-piece unit that is cheaper than any limited-slip or locker. It's also stronger, lighter, and has no internal parts to service (and is technically not a differential). The problem is that wheel speed (from side to side) differentiates when turning. A spool is fine for something like a drag car that does all of its forward motion in a straight line, but most vehicles need to turn left and right. When a vehicle turns, the inside (of the turn) wheels spin more slowly than the outside wheels. Without some type of axle differential that allows wheel speed differentiation, the vehicle will be pushed straight forward and the inside driven tire will chirp as it skips along.
This is why a limited-slip or locking differential is much preferred over a spool in a street-legal application. But which one (limited-slip or locker) is better for you? That's really a question of application.
Advantages of a Locking Differential
• True two-wheel drive per axle
• No servicing
• Extremely durable
• Bolt-in applications with zero axle, ring-and-pinion, or axleshaft modification
• Greatly enhances traction
Cons of a Locking Differential
• Wears tires out more quickly
• Front locker makes steering difficult
• Occasional banging/clunking of automatic lockers could give your grandma a heart attack
• Can make snow/ice driving more difficult
Eaton produces an automatically-locking differential called a Detroit Locker that does an excellent job of enhancing traction, and it fully locks when power is applied-something that gives true all-wheel drive, but it isn't always welcomed by a driver in a turn or in icy road conditions. The full-locking capability is integral in extreme driving situations though, and automatically turns the Detroit Locker differential into a spool when engaged.
Eaton also produces a helical gear limited-slip differential called the Truetrac. A limited-slip differential is one that limits the slip between the axleshafts (or wheels) when power is applied to the differential. Though these limited-slip diffs generally have better street characteristics than locking differentials, they do not completely lock both axles together, which can leave one wheel spinning and one wheel caught up if the situation is bad enough. On top of that, many limited-slip differentials use clutch packs that can eventually wear out.
You'll have to figure out which differential is best for you, basing it on your uses and your vehicular application. Generally, we tend to let the vehicle's intended use be the dividing line between a locker and a limited-slip-if it's more of a daily driver it gets a limited-slip. If it's more of a toy, then it gets a locker.
Advantages of a Limited-Slip Differential
• Enhances traction in all weather and road conditions, including ice and snow
• Tires won't "chirp"
• No accelerated tire wear
• Silent operation (unless servicing is required)
Cons of a Limited-Slip Differential
• Doesn't fully lock both axles together
• Can possibly be weaker (physically) than a locking differential, depending on the design
• Certain limited-slips can sometimes pull side to side in a front axle application