Get the
Hori one from Nippon Yasan. They're super cheap and absolutely fantastic, as expected of Hori. I currently use them on my New 3DS and I hardly see them
.
I suggest getting two packs in case something goes wrong. I didn't know about the bathroom trick when I applied the bottom filter, so some dust got in there and now I'll have to order a new pack
. The shipping costs are more expensive than the screen protector itself lol.
As for your second question, the New 3DS is slightly bigger than the OG 3DS so it may not fit in a case designed for the old 3DS. I use the new Hori (blue) hard case for my New 3DS and I love it. It's lightweight (only 85 gram), looks nice, durable and even has three pouches to hold some cartridges. I'll see if I can take a picture.
Edit:
At the moment I can only find the
black version on Nippon-Yasan's site, but maybe Play-Asia has the blue one in stock if you prefer that color.