Which trading platform is the most cost effective for trading US stocks in Singapore?

I'd prefer Td Ameritrade. Great interface, tools, mobile app. The mobile app is good enough to use if you know what you wanna get into without needing charts. Otherwise there's a great charting tool built into the desktop version.

No wonky fees required. You only pay something when you transact. And margin fees if you are holding stocks on margin.

Believe you can negotiate for cheaper comm rates if you transact sufficient volume.

For limited ETF selection and fund below 50k USD: kristal.ai (Robo)

For diverified selection (US/HK/SG) stocks/bonds/ETFs: Saxo

For higher investing amount >$100k : Interactive Brokers

For cheap fees + free stocks but a relatively new broker: Tiger Brokers

For Dollar Cost Averaging/ RSP: FSMOne

Hope this clarifies!