"Better" is kinda subjective territory, but I'll break down some of the differences. The cell counts in the cats are exactly the same, and both are pretty high quality. The Stainless Works kit is made from 304 Stainless Steel, while the Solo-Performance Catted Downpipes are made with 409, giving the Stainless Works kit a hardiness advantage in places with heavy salt. Now, one of the reasons why the Solo downpipes are so popular (despite being made from lower-grade stainless steel) is that they have a built-in resonator just before the cat-back connection, which helps eliminate drone, making them probably one of the quietest downpipe kits on the market. Performance-wise, it's kind of tough to say, as the gains you'll see from a given downpipe will largely depend on your choice of custom tuner.