I assume you're talking about staying on the centre line before you touch the ground, rather than after? The two problems are quite different but obviously related.
Wing-down is, IMHO, much much easier, but you must practice it with an instructor until you are happy with it. I find it easiest to start off crabbed. Then, at some stage (early on during final approach is easiest, but you can leave it later and later as you get more practice), use rudder to straighten the nose, and enough aileron to ensure you stay on the centre line.
The next bit should all happen sub-conciously, although it doesn't harm to know what's going on. As you get closer to the ground, the wind will become lighter and its direction will change. The lighter wind will probably mean you'll need less wing-down, although the change in direction might mean you need more. Then, as you start to round out, you'll slow down. This means that the wind will have more effect on you, and the controls will loose their effectiveness, so you'll need to increase the amount of aileron and rudder in order to keep the nose straight and keep the aircraft on the centre-line. Like I said, though, you won't be aware of this - you will just make some small control corrections instinctively to keep everything where it needs to be until the wheels are firmly on the ground. Scraping a wing, as Dude rightly points out, really isn't an issue at all.
I don't know if you have any plans to move onto other aircraft. If you move to a lighter aircraft, you will find that wing-low approaches become more and more important. The problem with the crabbed approach is that, after removing the crab, there is a small amount of time for the wind to begin to move you sideways. The lighter the aircraft, the more of a problem this is, and the more appropriate the wing-low approach becomes, although this is probably seriously over-simplified and you will learn what's best for each aircraft as you get to know the type.
Find a good instructor and spend an hour or two in a nice strong cross-wind!
FFF
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