This depends on what you’re mainly riding, but both work really well. For trails with lots of rock and roots we recommend the coil set up as it will smooth these out really well and for trails with lots of big hits the air will always feel more bottomless. Even with volume spacers the air shock does not feel harsh at the end of travel.
Using the spring rate listed below will provide more bottom out resistance than the stock link. The rates are calculated for 30% sag so you could go up to a stiffer spring without making it sit too high if you want even more.
The recommended spring rate listed below will also provide more small bump sensitivity than the stock link if the damping is properly adjusted, but if you would like more go down 50lbs in spring rate. We don’t recommend much lower than this because it will begin to make the bike sit lower in its travel than it should for pedaling. With the Evo this can make pedal strikes much more frequent since it has such a low BB. If you are shuttling or riding lifts you can go as low as you’re comfortable with though.
Any Stumpjumper (standard, ST, or Evo) that’s 2019 or newer is compatible with the link. If you have a 2018 find your bike in Specialized’s bike archive and make sure it’s frame is the same style as this one here: https://www.specialized.com/us/en/mens-s-works-stumpjumper-29/p/154955?color=253538-154955. Specialized switched Stumpjumper generations that year and consider both to be 2018 model years, so make sure it is the generation of frame that matches that.