Gatwick Express is the simplest option from Victoria with dedicated luggage space and onboard info screens

https://www.scribd.com/document/1077066259/Heathrow-to-Gatwick-Airport-Transfers-Coach-Taxi-or-Train-174457

Gatwick Express is the simplest option from Victoria with dedicated luggage space and onboard info screens. It costs more but minimizes stops and confusion for first-time visitors.