The Federation is clearly not a centrally planned economy, and therefore obviously not communist. Individual freedom of choice is very obvious. Everyone chooses their careers, and there are many mentions of this throughout the series — witness every single time someone waxes nostalgic about why they chose to enter Starfleet. Witness Bashir going on about why he wanted to be a doctor instead of a tennis player. Witness Wesley dropping out of Starfleet. Witness Vash being an archeologist and Kasidy Yates being a cargo ship captain.