What stock broker do millionaires use?

I'm curious to know, which stock broker do millionaires tend to use? Do they prefer a specific brokerage firm known for its high-end services and expert advice, or do they spread their investments across multiple platforms? Is there a common thread among the brokers favored by millionaires that sets them apart from the rest, perhaps in terms of accessibility, fees, or investment options? I'd love to hear your insights on this question, as I'm always looking to improve my own investment strategies and learn from the success of others.