Which glycolic acid toner should I choose?

The Ordinary Glycolic Acid 7% Exfoliating Toner is a little stronger. The PIXI Glow Tonic Toner with 5% Glycolic Acid is gentler, so it is a good first acid toner.

Glycolic acid or salicylic acid: which should I choose?

Glycolic acid exfoliates the surface of the skin for brightness and smoother texture. Salicylic acid works inside pores, so it suits blackheads and oily, blemish-prone skin.

Which glycolic acid strength should I choose?

Start with around 5% to 7% in a toner. Higher-strength treatments and peels are best once your skin is used to acids, and always wear SPF during the day.