Which is better for gaming?

The LG C5. It has 144Hz VRR, four HDMI 2.1 inputs and a 0.1ms response time, so it suits PS5, Xbox Series X and PC gaming better than the Samsung's 120Hz panel.

Does the Samsung S90D support Dolby Vision?

No. The S90D handles HDR10 and HLG but not Dolby Vision. The LG C5 supports Dolby Vision, HDR10 and HLG.

Is the LG C5 worth stepping up to over the S90D?

If you have the wall space, yes. The C5 gives you a 77-inch panel, Dolby Vision, 144Hz VRR and HDMI 2.1, which the S90D does not match.

Which has better voice assistant support?

The Samsung S90D. It works with Google Assistant and Amazon Alexa. The LG C5 relies on webOS 25 and LG's own AI features.

Both are OLED panels with similar lifespans. The LG's larger panel and higher owner rating suggest stronger long-term satisfaction, but neither has a clear durability edge.

Samsung S90D OLED 4K Smart TV vs LG C5 Series OLED evo 4K TV

The LG C5 is the stronger TV overall: a 77-inch OLED evo panel, 144Hz VRR, four HDMI 2.1 ports and Dolby Vision, backed by a 4.8 rating from over 1,000 owners. The Samsung S90D is a solid 65-inch OLED with 120Hz and four HDMI ports, but it is smaller and lacks Dolby Vision. Buy the LG if size, gaming headroom and Dolby Vision matter; buy the Samsung if a 65-inch set fits your room and you want Samsung's anti-glare panel and Google Assistant support.

Choose the Samsung S90D if you want a 65-inch OLED with a bright anti-glare panel, Google Assistant and Alexa built in, and 120Hz gaming.
Choose the LG C5 if you want a larger 77-inch OLED evo with 144Hz VRR, four HDMI 2.1 ports and Dolby Vision.

Prices

LG C5 Series OLED evo 4K TV: $1,680.25 at Walmart (last seen Nov 9)