OK I’m by no means scientific, but by a search through Amazon.com plus checking with Fakespot.com for spammed reviews, there are many of these, here are some recommendations for protecting your very valuable AirPods, so in order recommendations are:
Catalyst Waterproof case with Carabiner, these are the quite expensive at $25 (Amazon), but they get a B Rating from Fakespot.com and being waterproof is pretty neat. I ordered and will update when they arrive.
Netspower case plus accessories. At $10, it is hard to beat this bundle, the silicon case is decent, there is a big pouch and just about every little silicon dohickey that you can imagine. It includes black and white versions of cords to hold them while running as well as black and white version of ear clips if they tend to fall out. For me, these are fine, but the main problem is the lack of a carabiner so that when you are not wearing them the charging case doesn’t walk away. It has an A Rating from Fakespot which is pretty remarkable.
Elago AirPod hang case. Another $11 purchase that is hard to beat, but since I got it, it has fallen to a C rating. The main issue I think is that the carabiner is held on with a little bit of silicon so easy to break off.
VIMVAP magnetic cord holder. This $10 string was highly rated, but now has failed to a C Rating on Fakespot, having got it, it is OK, but the magnetic part doesn’t seem very reliable and the thing isn’t easy to snap together.