APO means apochromatic glass, typically considered a higher grade.

SLD means special low dispersion glass, which is their terms for high performance glass.

DG means the lens is specially coated to reduce reflection on digital cameras.

I have the second lens you listed for the Pentax mount and I've used it quite a bit. It generally works well, but there's a tendency for the autofocus to hunt a lot with it. That's partly my camera as well, Pentax AF is not noted for its speed, but in comparison to my other AF lenses, this one hunts the most. As Alan noted, it's not a "true" macro in the sense that it doesn't give 1:1 or better magnification, but it does allow close focus and you get some nice, close, shots with them such as these:

Just be aware that with both of the lenses, the rear element extends and you can't use a Sigma teleconverter on them. It also looks like Sigma may have replaced these lenses with a new one, but it's magnification ratio is much less, though you do get optical stabilization.

Anyways, the second lens listed is a good, budget, option for starting into macro. Eventually, you'll want to get a 1:1 or better lens, but learning the ropes on the Sigma lens is a good place to start and you also get a solid telephoto length at the same time. By the way, once you do look to get another, don't hesitate to look at places like Craigslist for older lenses, in macro you're very often going to be manually focussing, so some of the older, manual lenses, with 1:1 macro will work great and cost little.