The shock absorber is much better IMO. Putting a length of pipe above the valve on a T works and is a classic fix. However, under that pressure, air will be absorbed by the water eventually. When the water reaches the top, you have to turn off house water and open an outdoor spigot - something lower than whatever is hammering again anyway. The water in the cavity will drain out and you have your shock absorber back. For awhile.

Also, the shock absorbers are easier to install after the fact - you can put them on the line in a crawl space, preferably semi-close to the hammering valve. Even under the sink is doable. There's a piston that compresses the air, so water can't run into the cavity. I still slope them upwards from the pipe, if it's horizontal, based on pure superstition. Putting an empty length of pipe above valves usually would require taking sheetrock or tile out.

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1986 300SDL, 362K
1984 300D, 138K