Musk announced the potential deal after turning down a potential board seat at the company.
UBS ranks highest in overall investor satisfaction with a score of 777, and Vanguard (759) ranks second.
She sold 185,900 shares of Twitter on April 11, one week after Elon Musk revealed his 9.2% stake in the company.
Celebrities on the investor roster include Ashton Kutcher, Justin Bieber, Steve Aoki, and Gwyneth Paltrow.
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Robinhood's is among the worst high-profile global stock market debuts since the onset of the pandemic.
Billionaire Peter Thiel blamed the finance titans for the digital currency's failure to reach $100,000.
The company's wallet enables users to interact with crypto outside of Robinhood's trading platform.
He also reiterated a call that bitcoin will reach a price of $500,000 and eventually $1 million.