Great suggestions so far. I'd also submit the
Incase Icon sleeve, which I have been using for a few weeks now. Here are a few of my own observations about this sleeve:
- Well made, good build quality
- Fits the 13" MBPr like a glove, almost literally (which is generally a good thing, but it can be a bit difficult to remove the MBPr from the sleeve at first until it breaks in a bit)
- Provides very good protection for a sleeve, a lot of which is owing to a rubber ring that runs around the perimeter of the sleeve (which, unfortunately also adds a good ~1.5 inches to the width of the MBPr)
- Vertically oriented, meaning it loads from the short side of the MBPr (which could be advantageous if you're carrying it in a backpack or other vertically oriented bag, but could be cumbersome if you're carrying it in a briefcase or other horizontally oriented bag)
- Expensive (~$70 at the Apple Store)
If you plan to tote your MBPr in a backpack that doesn't have a dedicated laptop compartment (or one that is oversized for a 13" laptop where it tends to flop around a bit during transport), then I think this is an excellent sleeve for that purpose.
EDIT: Perhaps you have seen the sticky thread at the top of this forum that is dedicated to this question? Admittedly, it is over 2,800 posts long at this point, so it's kinda hard to wade through all of it.
https://forums.macrumors.com/threads/1391592/