As to the “best”, someone else probably knows better than I, but adding sulfur is probably the easiest and most straightforward. Test your pH, then amend as needed to get into the right range. The granular sulfur you buy will likely have the Table and directions right on the bag for determining the right amount. I know peat moss is another option.
Good luck, I hope this helps.
“Best” is probably sulfur, but “easiest” is to just plant them under a pine tree, or take the decomposing pine needles from under the tree and use it to mulch the blueberries with.
I’m holding off on blueberries until my pines are bigger for that reason, although if I find a really good deal I might just see if I can get some needles from a christmas tree farm.
Right now my biggest pine tree is a stately 8 inches tall :p