I use the regular. I don't bake it.
If I need more oomph, I have a box of Arm & Hammer's "Super Washing Soda" which is baked baking soda.
Washing Soda is sold in the detergent section of the supermarket in a big yellow box.
I have a reactor, so i just use it to make adjustments, but I bake it, and use store brand. I didnt know that Super Washing Soda was baked. I might pick some of that up.
Un-baked will not raise your pH, but baked will. That is really the only difference.
As far as using the Washing Soda, you may want to check, but the regular baking soda is food grade which may be a higher grade of purity than the washing soda is.