What is the best card for lounge access?

I would take any $120K card with unlimited priority pass as my chocie pick. Some have guesting benefits which is good when travelling with a companion.

However, if you don't qualify for a $120K card, then a number of $30K cards will give the same benefits, but capped at 2 visits a year. Some good examples are the Citi PM and DBS Altitude. Sign up for both cards doubles your visits, so there's no real harm holding both.​​​

A full listing of credit cards in Singapore that provide lounge access can be found here: https://milelion.com/2019/09/28/which-credit-ca...
In general, you're looking at 2 or so free visits unless you qualify for a $120K card, which may offer unlimited lounge access. You'll have to pay ~$500 in annual fees, but you may earn it back through lounge access, miles with the annual fee and other perks.