Which is better glycolic acid or salicylic acid

Salicylic acid is more keratolitic (it helps to uncloge pores), exfoliating properties are mild. AHA (including glucolic acid) have sronger exfoliating effect. But be careful, skin on the neck is usually quite sensitive to high percentage of acids.

Glycolic acid is better. Your neck has thinner skin and not as many sebaceous glands. So proceed cautiously.

Different acids do different things , depending on what my skin needs at the time......I love using both !

I personally like glycolic acid more but it's a very personal thing depending on what your skin needs and what you want to achieve

SA for oily skin, and GA for dry skin