I normally carry a speed strip - if I feel the need to carry a reload. It's not something you'll realistically ever need in an armed citizen self defense shoot, but sometimes more rounds make you feel better...
If I carry a speed loader, I carry it in one the slip over holders from Wild Bills Concealment. They allow you to slip either 2 or 3 rounds over your belt, which reduces the profile and makes them less noticeable. They've proven to be comfortable and secure in use.
I have them in 5 round J frame, 6 round K frame and 7 round L frame sizes for my HKS speed loaders with .38s and .357s.