I have a H6 battery in my MK7 GTI SE that I put on a few years ago. Not sure why I chose H6. Should I replace with same size or H5?

I ask because using Costco's battery selector gives me the result of H5. I bought the H6 from walmart a few years ago but not sure why I did that instead of buying the H5. Anyways should I just stick with another H6 or get the H5 from Costco since it's cheaper?