I have a Giant Trace X3 2012
It has 26" rims. Which of these spokes type do I need for my bike? Strongest or best match for the spokes I already have.
DT Swiss Champion Stainless PG Spokes DT Swiss Champion Stainless DB Spokes
The difference is whether the spoke is butted or straight gauge.
A butted spoke is thinner in the middle, which allows more flexibility without damaging the wheel, which usually makes it the stronger, as well as the lighter choice. The choice is purely personal, though, and either will function as long as the lengths are correct. Note that not every spoke in a wheel set is the same length.
Note that there are several parameters to spokes:
For replacement spokes the two critical dimensions are the length and the head/nipple diameter. Ideally one should also match double-butted or not, but it's not critical. Re length, the spoke should catch at least 6 threads (6 full turns) of the nipple, and it absolutely must not poke through to where the spoke end can contact the tube (even with a rim strip in place). You generally have the ideal length when you can see 2-3 threads above the top of the nipple.
Note that, as Zen also mentions, the spokes on the back wheel will almost certainly be two different lengths (left side vs right), and the spokes on the front are likely yet again a third length. "Fancy" wheels can have even more lengths.
There are charts and "calculators" available online that give spoke length for various standard wheel configurations (wheel diameter, hub diameter, "cross" count of the spokes, etc). They're pretty good but may be off by a mm or two for certain hub/rim combos.