Some years ago, because I was told peat moss would lower the soils pH, I worked 3.8 cubic feet of peat moss into a 4 x 4 planting bed with a soil pH of 5.7 with the intent of planting blueberries there. The following spring a soil test told me the soils pH now was 7.2, so I had to and still need to, use sulfur to keep the soils pH low enough to keep the blueberries happy.
Most allof the commercial blueberrie growers around here use either sulfer or aluminum sulfate to keep the soils pH low enough.

If you intend to plant and grow blueberries in easrnest, you should have your soil tested before applying much of what will affect its pH. Peat moss, with a very low pH on the acid side, will not dramatically change your soil if it is anywhere near neutral, it can help acid loving plants when the soil is near the level they prefer.
Garden sulfur will do that.....but garden sulfur takes time to work its magic and it can increase/decrease very quickly so you should be very careful about how much you add.
Get a soil test done. Most large nursery operations will do it for a nominal charge. If not there, then your local state funded university's agricultural dept.
Usually, acid loving plants such as rhdoodendrons, will have the garden sulfur added in the spring, first thing, and the pH monitored by the way the plant acts toward the soil's acidity. Too much/too little shows up on the plant...usually in the leaves. It can be a cue to either reduce the effects or increase.

Sometimes large nurseries can be trusted to sell soil testers reliably enough to give the home gardener a trustworthy test result. Its not professional but then you're not a professional either are you.

If there is someone in your area growing blueberries in soil like yours, then that person might be willing to share what they did to be successful. Blueberries grow well in soils with high organic matter, such as peat moss, or compost made from shredded tree leaves. There are fungi living in the soil, and around the roots, of blueberry shrubs, and the fungi require organic matter as food. You will need to know the pH of your irrigation water. If you are on a municipal supply, there should be an annual water report on record, and that document should give the pH. If you are using well water, then you will have to have it tested for pH, unless you know for sure that the water is free of calcium carbonate. If you are able to collect rainwater in quantity, and use this on your blueberry shrubs, then you don't have to test the water for pH, because rainwater is always neutral or slightly acidic. Blueberry shrubs must be kept watered during a drought, and I always have to water for a week or two in July or August. I end up using between 100 and 200 gallons per shrub, per season. That is enough water to significantly raise soil pH, if the water is hard. Here in Madison, Wisconsin, our native soil is high in clay, so I mix in composted tree leaves 50/50 by volume, when preparing soil for blueberries. I also apply agricultural sulfur, both in the bottom of the hole, and around the shrub, on the surface, but under the mulch. However, our native soil has pH = 7.6, very likely higher than the pH of your native soil. I am using bromocresol green indicator to measure soil pH, and I can provide more information if you are interested. If you have soft water, and naturally acidic soil, then you might not have to be concerned with pH.

Thanks! You're right, I should check the pH of the soil and water first. If it's not excessively high, a trial planting should show whether any change is needed.

Sounds like sulfur is the usual amendment to lower pH, but peat might also be effective.

Peat moss has a small affect on soil pH. It will not overcome or counteract the effect of irrigation with hard water. But peat moss will support the growth of soil fungi, and these fungi feed the roots of the blueberry shrub, so peat is a helpful soil amendment. Other forms of vegetable fiber, like composted tree leaves, have the same effect. If you soil has pH over 6.5, you will likely have to use sulfur, ammonium sulfate, sulfuric acid, or aluminum sulfate to lower soil pH and keep it down. Here in the midwest, soil & water pH testing is necessary. But, if you know someone locally who raises blueberries in local soil, with local water, you might be able to proceed without testing.

I'm growing blueberries and know exactly what you are going through. I Made a raised bed using peat moss and compost and then planted my plants. The results were not happy ones. They didn't grow one inch and produced very few berries. So I did a soil test and was amazed that the pH was 6.9. So after discussing the matter with the co-op experts I added sulfur in increments in the summer, fall and finally I'll add the final addition in the spring. The expert also said to apply the hollytone plant food as suggested in the directions. So that's what I'm doing. I won't know the results until next summer when the blueberries should be producing. I've got my fingers crossed. The Expert did say to stay away from the peat moss and to make sure I watered the blueberries regularly. He said that if I wanted to top dress the bed to use pine needles and that's what I did.

Maine (native lowbush) wild blueberries grow in the most inhospitable soil you can imagine. Mine grow on granite ledge. The soil is dry, shallow, powdery, and acidic. We harvest in August, then mow and burn the field to the ground the following (fallow) year. Not that this is of any use to you, because the way blueberries are treated in the rest of the U.S. is totally foreign to me.

You have to start with a reasonably accurate soil pH reading to use as a benchmark.
The short answer to your question is to do both. Blueberries do best in soils high in organic matter- to increase organic matter till in such items as peat moss, sawdust,bark, leaves, manure or compost.

Blueberries like a soil pH somewhere in the 4.5-5.5 range and the cheapest(not fastest) way to do this is to till in some sulphur. Michigan State Extension has some great information concerning lowering the soil pH. I'll copy one such url. Your preperation for the blueberry patch is going to teach you patience but it will be better and faster if you do every thing as correct as you can before you plant the blueberries in their permanent home.

http://www.canr.msu.edu/vanburen/fsulfur.htm

Gary