There are a ton of options when it comes to cryptocurrency brokerages. For new investors, Coinbase is a great option. Coinbase has a free cryptocurrency conversion feature where you can trade your crypto for any other token supported by Coinbase.
Other crypto brokerages that are solid options for intermediate traders are eToro, Binance and Gemini. Robinhood also supports certain cryptos but the platform only supports trading for 5 altcoins.