Everything you need to know:
https://www.kester.com/
The "best" flux may depend on your solder. Cored or non-cored? Lead free or not? The Kester site seems to address those variables.
I use Kester "44" rosin flux-cored 63:37 leaded solder in 0.031 for TH and 0.015 for SMD (with some exceptions).
For a separate flux, I use paste flux Kester SP-44. My 2-oz tin is of unknown age and is only about 1/3 used. "A little dab will do you." It lasts a long time and works well with small SMD's like you are describing. I also clean flux residue with a solvent afterwards.
John