Neither.
Kent RO Right buffers both in one product so you can't control the balance.
Seachems Equilibrium well, I hate the stuff based on using it.
I use GLA Ultimate GH Booster
GLA booster is so close to the seachem product I can't tell the difference in tank except,,, Equillibrium turns into a brick in the container and can take days to fully mix into the tank. GLA Ultimate GH booster is ground much finer and mixes better.
Cost factor is better too.
KH buffering is done with Arm & Hammer baking soda. It provides consistant results for raising KH and I mix for 2dKH both injected and low tech alike giving me a neutral 7pH.
I've used A&H baking soda for KH and have for years with consistent results.
These are the reference volumes I use.
To increase KH
1/8 TSP : 6.4gallons = 1dKH
1/4 TSP : 13.2 gallons = 1dKH
1/2 TSP : 26.4 gallons = 1dKH
these measurements are in leveled spoons, use a cc or other straight edge and scrape the top of the spoon after filling it so it's full but no piling of powder above the edge (hope that made sense LOL)
Tests I feel I needed for basic mixing; TDS pen, chemical drop tests for GH and KH.