Depends on department.

Got friends working 9 to 6, rarely OT. But also got friends OTing alot, esp in operations

Also depends on project

Credit Suisse is a BB so it's hands down best of the 3 in terms of pay, prestige and career opportunities. Rabobank is a large European bank with a global presence while OCBC is a local bank with less than half of Rabo's market cap and hardly any presence outside of SEA and maybe Greater China. Credit Suisse and Rabo are global brands while hardly anyone outside of Singapore know what's a OCBC.

My view only (feel free to disagree):

In terms of exposure/learning: CS > Rabo > OCBC
In terms of internal promotion/progression: OCBC > CS / Rabo (generally harder to promote in foreign banks)

That's because local banks are known to have serious title inflation. Half the bank is AVP and above, which is ridiculous if you think about it. Foreign banks have titles that more closely reflect the role and responsibilities of the job. The local banks know that their pay packages are not as competitive as the big international banks so they try to compensate by giving you a nicer title.