Which is better for gaming?

The Quantum Pro. Its 120 Hz refresh rate and four HDMI ports handle consoles better than the M55Q6L4's 60 Hz panel and three ports.

Do I need Wi-Fi on a TV?

Not strictly, but the M55Q6L4 connects only by Ethernet, so you need a cable run to your router. The Quantum Pro adds Wi-Fi 6E and Bluetooth.

Which has better picture quality?

The Quantum Pro adds local dimming on top of QLED and HDR, which usually means deeper blacks and better contrast. The M55Q6L4 is QLED with HDR but no local dimming listed.

Is the Quantum Pro worth stepping up to?

Yes for gamers and people who want wireless streaming or voice control. If you only stream shows over a wired connection, the M55Q6L4 covers the basics.

Neither has a documented reliability edge. The Quantum Pro has more owner reports, including some edge darkening, while the M55Q6L4 has little owner feedback to judge by.

Vizio Quantum Pro 4K QLED TV vs VIZIO M55Q6L4 55-Inch QLED TV

The Vizio Quantum Pro is the better TV for most people deciding between these two. It doubles the refresh rate to 120 Hz, adds Wi-Fi 6E and Bluetooth, gives you four HDMI ports instead of three, and supports Google Assistant and Alexa. The M55Q6L4 is a 60 Hz set with wired-only networking and no smart assistant support, so it suits a buyer who mainly streams and does not game. Owners rate the Quantum Pro well on picture and value, though some report noisy standard-definition playback and edge darkening.

Choose the Vizio Quantum Pro if you game, watch sports, or want wireless streaming and voice control without extra hardware.
Choose the VIZIO M55Q6L4 if you want a basic 4K QLED for streaming and will connect it by Ethernet.

Prices

VIZIO M55Q6L4 55-Inch QLED TV: $298.00 at Walmart (checked today)