I bought this case a week ago and it works like a charm! It's really cheap, and fits my XL perfectly! All of the negative reviews are people with 3DS originals saying the case is too big, lol.
When I ordered my 3DS XL from walmart, it came with a free case that also holds 12 games. I wasn't all too thrilled about it at first because it looked a little young for me (I'm 21), but it quickly grew on me and I love it. Plus it has a little Mario design and the zipper says "Super Mario". Can't beat a throwback like that
I have a few, I usually order clear plastic ones from eBay and customise them or use them over a vinyl decal, never had any scratching issues. I also have an aluminium case, lined with fuzzy fabric and no scratching either, but some people have reported a poor fit, mine is perfect though. I have a case similar to the Nintendo one posted by runekey but it's blue, I really love it and it does a fab job, I can fit the console in with a hard case on it too (overprotective....)
For the AC console, I'll be using a clear plastic case with a skin over the console to try to keep it clean. It'll be in and out of my handbag so anything that prevents white from getting dirt nearby will be a godsend!!