I use a boar hair brush most of the time, and I’ve found that CosmoBarber’s Precision Loading Method works wonders. Just be sure to give the boar a good soak (at least 5 minutes but I sometimes do 15-30) beforehand.
This is what I tend to do, but mostly because I don't like the thought of getting my tubs all messy. I know it's a stupid reason, but it's my stupid reason.
I will just load my Stirling samples in the dollar tree tins, though. Really great for travel too.