Which bank (DBS, OCBC or UOB) is better for CPF investment account for CPF OA investing? If I buy SG listed shares with CPF OA, will they be held in custody or CDP account?

Can all local stock broker link with cpfia or those selected ones only like dbs vickers, ocbc securities or uob kh?

UOB is the cheapest, as Elijah pointed out. The shares or instruments are either held with the agent banks, or the investment administrator.

Just FYI, you can only invest 35% of your investible CPF monies in stocks, but you can invest in 100% unit trust. Endowus offers exlusive access to 2 vanguard fund for CPF investments at the lowest fees, do find out more here!
https://endowus.com/insights/webinar-cpf-invest...