How many serums do you use?

I’ve just turned 30 and am late to incorporating serums as part of my daily routine.

I was wondering:

What are your holy grail serum(s)? Do you use the same one(s) every day, or rotate during the week? Or do you jump between different brands depending on what your skin needs or depending on the season?

I currently am starting out with Shiseido Power Infusing Concentrate and Tatcha Silk Serum. However I’m happy to be influenced!

Thanks in advance!