Which is better for a bright living room?

The LG C6. Its Brightness Booster and a11 processor are built to raise OLED brightness, and it adds Dolby Vision for more HDR sources. The Samsung S90H is also OLED, but its listed HDR support stops at HDR10+.

Which is better for gaming?

Both list 165 Hz panels. The LG C6 also lists VRR, G-Sync, FreeSync Premium and a 0.1ms response time, so it is the safer pick for console and PC gaming. The Samsung's sync features are not listed.

Is the LG C6 worth stepping up to over the Samsung?

If you have room for 65 inches, yes. You get a much larger picture, Dolby Vision, four HDMI inputs and 2.2-channel sound. If your room only fits 48 inches, the Samsung is the right size.

Which has better sound?

The LG C6. It has 2.2 speaker channels with Dolby Atmos and AI Sound Pro. The Samsung S90H has two speakers with Dolby Atmos. Either benefits from a soundbar.

Which smart platform is easier to use?

They are close. LG's webOS adds Google Gemini and Copilot for voice search. Samsung's Tizen adds Bixby and Alexa. Pick the assistant you already use.

Both are OLED, so burn-in risk depends on how you watch. LG lists OLED Care to protect the panel, which the Samsung listing does not mention. Neither brand publishes a lifespan figure.

LG OLED C6 65-inch TV vs Samsung S90H OLED 4K Smart TV

These are different sizes first: the LG C6 is a 65-inch OLED, the Samsung S90H is a 48-inch OLED. Buy the LG C6 if you want a big-screen OLED with four HDMI 2.1 ports, Dolby Vision, and LG's webOS. Buy the Samsung S90H if 48 inches fits your room and you prefer Tizen with Bixby and Alexa built in. Both are 4K OLED panels with 165Hz-class gaming support and Dolby Atmos, and both rate highly with owners.

Choose the LG C6 if you want a 65-inch OLED with Dolby Vision, four HDMI inputs, and LG's webOS with Google Gemini and Copilot.
Choose the Samsung S90H if a 48-inch OLED suits your space and you want Tizen with Bixby and Alexa built in.

Prices

LG OLED C6 65-inch TV: $899.99 at Amazon (last seen Nov 12)
Samsung S90H OLED 4K Smart TV: $997.99 at Walmart (checked today)
Difference: the LG OLED C6 65-inch TV is $98.00 cheaper than the Samsung S90H OLED 4K Smart TV at the latest prices (Nov 12 and Nov 13)